Sprint Galaxy Note 5 keeps saying invalid SIM when using AT&T SIM card, other issues

Today we try to discuss what it means to have an unlocked phone and what to do if faced with a problem with it. This is far from a detailed explanation on the subject about why some unlocked phones may not work in other networks but we hope that we can shed some light on the matter.

We also cover two other issues so hopefully Android community will find this post helpful.

If you are looking for solutions to your own #Android issue, you can contact us by using the link provided at the bottom of this page.

When describing your issue, please be as detailed as possible so we can easily pinpoint a relevant solution. If you can, kindly include the exact error messages you are getting to give us an idea where to start. If you have already tried some troubleshooting steps before emailing us, make sure to mention them so we can skip them in our answers.

Below are specific topics we’re bringing for you today:

Problem 1: Sprint Galaxy Note 5 keeps saying invalid SIM when using AT&T SIM card

My phone is paid off and supposedly unlocked by Sprint. I went to AT&T to switch and they said my phone is compatible. When AT&T put their SIM in my phone, it says invalid SIM. They put my phone in their system and it came back compatible. The manager of AT&T feel it’s not completely unlocked by Sprint. Sprint sent me an email saying the phone was successfully unlocked. Can you give me some answers of what may be the issue? — Clara Sanders

Solution: Hi Clara. There are a few things that you must know to help you identify the reaons for your problem. Let’s discuss them briefly.

What “unlocked” phone means

A lot of users like to think of unlocked phone as being always compatible with all networks. Sadly, that’s not the case. An unlocked phone, in your case an originally Sprint device, means that its software has been slightly modified to allow it to send and receive SMS/MMS, make/receive voice calls, and probably allow mobile data. In other words, the operating system has been changed to let you use basic network functions but that’s it.

The bulk of the software is still Sprint, including the pre-installed apps. You won’t be able to use Sprint apps that require Sprint services anymore and updating to the latest available Android version is out of the question. These are some of perks that you have to give up for switching to another network. You don’t suddenly have an AT&T phone once you the device unlocked and AT&T SIM inserted. Basically, the phone is still deeply Sprint in nature. And that’s not to say everything network-related will work perfectly. We’ve heard of some cases wherein mobile data settings remain unchanged so MMS and data connection can’t be used at all.

Needless to say, unlocking only changes a small aspect of the phone (hardware remains unchanged obviously). Don’t think that you’ll be able to enjoy all AT&T network offerings as if you have an original AT&T device. Remember, your phone’s software is mainly third party and will most likely not work with AT&T’s system.


Another good point to discuss here is the differences between CDMA and GSM. In the United States, these are two most commonly used mobile technologies. Sprint, Verizon, and US Cellular use CDMA while AT&T and T-Mobile GSM.

CDMA devices don’t normally use SIM (Subscriber Identity Module) cards as subscriber information are embedded deeply in the software of the phone itself. Information such as your name, billing details, addresses,and all other subscriber specifics are programmed within the phone’s software. (CDMA phones can still sport a SIM card slot to allow them to use 4G LTE, which is a modified GSM technology.) While this is a more secure approach in terms of keeping personal details of the account holder, it also renders CDMA phones very difficult to “reprogram” to allow it to work with a different network. This may be the reason why you’re experiencing an issue at this time.

GSM phones, on the other hand, does not require reprogramming of the phone’s software except during the unlocking phase. And even that is relatively easier compared to that of CDMA phones. Once a carrier has unlocked a GSM phone, a user just needs to insert a compatible and active SIM card from another carrier and everything should work fine network-wise.

In general, CDMA phones won’t work with GSM networks or in another CDMA network, while GSM phones can work fine with most GSM networks. GSM phones may not work with CDMA networks too.

Unlocking process can be tricky

As mentioned above, reprogramming a CDMA device is not easy. While carriers can do the unlocking process for free as long as you no longer have any contract obligations with them, not everything may work as expected. Even if Sprint has properly unlocked the phone already, AT&T’s network may not be fully compatible with your phone’s hardware or current software. Unfortunately, only the two carriers can advise you on what the deal really is so you may need to work with both of them to get to the bottom of this issue. We know that’s not ideal but there’s no way for a third party support team like us to know where the problem lies. Procedures in unlocking (on Sprint’s side) and provisioning (on AT&T’s side) are proprietary so we have no accurate information on how to do them properly. We understand both carriers are claiming to have already tried their best and did the proper procedure but surely, one of them is at fault.

Get help from third party shops

Unlocking a device requires specific knowledge and professional tools so if you can’t get effective help from both carriers, consider getting help from shops that unlock phones.

Problem 2: Galaxy Note 5 won’t accept screen unlock PIN

To whom this may concern. I am struggling to enter my phone (Note 5). Last night (October 31st 2017), I went to sleep while my phone was downloading the newest update. This morning I entered my PIN, but could not enter. I do not know if maybe I forgot it, but whatever I try does not work.

I tried entering in safe mode, and I cleared cache, but still could not enter. I read online maybe factory resetting may work, but I do not want to lose all of my files. I also do not have a samsung account. Since I can’t get in my phone I do not know a way to back up my data otherwise. — Luke

Solution: Hi Luke. There are only three effective methods to gain access to an unlocked phone and they are by:

  1. unlocking your Note 5 using  Android Device Manager
  2. unlocking your Note 5 using Samsung Find My Mobile
  3. unlocking the device by performing a factory reset

Unfortunately, if the first two options are not applicable you have no other choice but to do the third, factory reset.

Problem 3: Galaxy Note 5 connected to wifi no internet

Hello. I have a Galaxy Note 5. My wifi says that it is connected, but when I try to Google search, open an article in Facebook, or play a game that requires internet, it won’t work. I have restarted my phone twice and tried using a different network. Nothing has worked.  Any suggestions? Is it time to get a new phone? P.S. I don’t really know what android version my phone uses, but it wouldn’t let me leave it blank. — Kristi Van Eaton

Solution: Hi Kristi. Below are some of the things that you can do to troubleshoot wifi connectivity.

Check if router is working

This is an important first step to determine where the problem lies. It’s possible that your router is malfunctioning, or there’s an issue with your Internet Service Provider (ISP). Needless to say, knowing whether the problem is with your phone or router is paramount. To do it, try to see if another wireless device like a laptop or another smartphone has internet connection when connected to the wifi you’re having trouble with. If all other devices can connect to the internet while using the wifi network you’re having trouble with, the most likely problem is in your phone.

Disable Power Saving Mode/Ultra Power Saving Mode

Samsung’s Power Saving Mode (may also be called Medium Power Saving Mode in some devices) or the more drastic Ultra Power Saving Mode (may also be called Maximum Power Saving Mode) disconnects wifi by default so be sure to turn wifi on again if that’s the case.

Forget wifi network and reconnect

Sometimes, wifi service may use old or outdated network information resulting to an issue like yours. To fix the problem, you can do the simple step of deleting old wifi details so the phone gets updated information about your wifi. To do that, follow the steps below:

  1. Open Settings app.
  2. Tap Connections.
  3. Press and hold Wi-Fi.
  4. Press and hold the wifi network you’re having a problem with.
  5. Tap Forget network.

After the network has been forgotten, restart your phone before attempting to connect.

Keep wifi on

There’s a certain wifi that few Android users notice and it’s called Keep wifi on during sleep. This feature gives a user flexibility how his/her wifi function works even when the screen is off or if the phone is hibernating (sleep). If you want, you can let wifi stay on even when the phone is hibernating to prevent losing internet connection. Here’s how:

  1. Open Settings app.
  2. Tap Connections.
  3. Press and hold Wi-Fi.
  4. Tap ADVANCED.
  5. Tap Keep wifi on during sleep.
  6. Select Always.

Factory reset

If all these suggested steps above won’t help, don’t forget to do a more drastic option of wiping the phone back to its factory defaults. If you haven’t tried it yet, here’s how to do it:

  1. Turn off your Samsung Galaxy Note 5 completely.
  2. Press and hold the Volume Up and the Home buttons first, and then press and hold the Power key.
  3. Keep the three buttons pressed and when ‘Samsung Galaxy Note5’ shows, release the Power key but continue holding the other two.
  4. Once the Android logo shows, release both the Volume Up and Home buttons.
  5. The notice ‘Installing system update’ will show on the screen for 30 to 60 seconds before the Android system recovery screen is shown with its options.
  6. Use the Volume Down key to highlight the option Yes — delete all user data and press the Power key to select it.
  7. When the process is complete, use the Volume Down key to highlight the option ‘Reboot system now’ and hit the Power key to restart the phone.
  8. The reboot may take a little longer to complete but don’t worry and wait for the device to become active.
  9. Set the phone up again and make sure to install any pending Android update.

Have the phone repaired or replaced

Should nothing above won’t help at all, there must be something wrong with the phone’s hardware. Consider sending it in for repair, or better yet, have it replaced.


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