Swapping SIM Windows to Android on same plan


I have a postpaid account using an old Lumia 640 Windows phone. I have purchased a new Pixel 4a 5G and I would like to just switch the SIM from one to the other (by reducing the card to the smaller size). I need to make sure it’ll be OK because I will not be able to return the smaller card to the old phone if it isn’t.

The new phone is already configured with everything, apps, settings etc. I don’t want anything other than the phone# and service plan info to transfer to the new phone. I know the contents are not compatible, but can anything on the card mess up the content/settings of the new phone?



13 replies

Userlevel 7
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You’re better off using the new sim that came with the Pixel 4a5G .

Buy or change SIM cards | T-Mobile Support



I know, but I have a problem.

I have had nothing but trouble with incompetent T-Mobile “experts” -- hours on the phone, ignorance and stupidity. They emailed me a blank QR code for a eSIM that does not work and I don’t want to wait until they mail a SIM.

I was planning to go to a store, but most stores here are closed until 30th (of course) and my old phone loses signal.

So the question is can I swap the SIM temporarily until the 30th and get a new eSIM set up at a store on the 30th?

Userlevel 7
Badge +13

Yes you can cut the sim to fit but you may not get full use of the network,

Out of curiosity why are the stores closed till June 30th?

Also you can contact Tmobile support using messenger on one of their social media accounts to see if they can help.


I want nothing more to do with support. Hours on the phone, ignorance and stupidity. Just wrote a letter to Sievert. Been a customer for more than a decade and it’s never been so bad -- the bigger they became, the worse.

They’ve been closed for weeks -- no idea why. There’s a note on the window “retail changes” or some such.


I assume that you have already followed these steps!


eSIM settings: Google Pixel 4a 5G | T-Mobile Support


eSIM is the way to go. Don’t cut SIM card unless you have a cutting utility. If the SIM card bends, it won’t work on Lumia either.


Yes, that was the intention. But…

The support agent asked me what device I had and I said Android Pixel 4a 5G. She instructed me to download some app from Google play that would configure an eSIM but there was none. She then emailed me a QR code and asked me to download a scanner from the store, we tried 2, there were some problems, but the eSIM profile was “blank” -- no phone# and plan -- so it does not work. I then checked: the app exists only for Apple and when I wanted to tell her she was gone.

So now I have a “blank” eSIM and no way to configure it with phone# and plan -- and I don’t want to call CS a fifth time. Note that your instructions require that the service had been activated and I have no idea whether she did or not. A mess.

I wanted to have the store clean the mess and set up an eSIM with a temporary new number, then later transfer the old number to a new eSIM later. But since they are closed, I thought of swapping the old SIM until they open and set up a new eSIM with the old number when they do.

What I need to know is (1) what do you mean “not full use of the network”? and (2) whether the

old SIM may mess up anything on the new phone setup.





Userlevel 7
Badge +13

Since you have a Pixel try going to in the settings to Network & Internet , Sim and hit the add button and there’s an option to add a number using an esim.

I don’t know if it’s on Android 11 because I’m running the Beta Android 12.


No, there is no such thing.

They have an app for Apple, but they have nothing for Android -- that’s why the agent was clueless what to do. If you read the T-Mobile online instructions, they are unclear. If she was supposed to email a code -- and I’m not sure of that -- my guess is she should have included the phone# and plan. Without that eSIM won’t work and without an app I can’t add them.

Userlevel 7
Badge +13

It must be something new for Android 12. You can sign up for the developers program and download Android 12(S) and try to see if the option is there.


No, as I explained, no way is this a solution to the problem. Besides I am new to Android, I barely learned to get by with 11 and I intend to defer 12 as much as I can -- I cannot afford to dedicate myself to learning versions of android -- some of us have real work to do.

I only wanted to know if there were problems swapping phones and if so, what. But it looks like I will have to wait until the 30th and go to the store. Ah, well -- technology was supposed to make us more efficient/productive but the human brain is a limiting factor.




“The app can only activate a T-Mobile prepaid line.
For postpaid accounts, check out T-Mobile eSIM.
Only available for Apple iPhone XS or newer running iOS 12.1.1 or later.”


So there is no app for Android, which means that she did not know what she was doing.


Should be clear from instructions for Android that you should get a QR code with the full eSIM

profile because there is no app.


Use these steps to download your eSIM settings. You must contact your carrier to activate service first.

To set up your eSIM as the first line on your phone:

  1. Remove the physical SIM from your phone prior to starting up.
  2. Make sure you’re connected to the internet through Wi-Fi.
  3. When you see the screen Connect to mobile network, tap Don’t have a SIM Card? > Next.
  4. Choose your carrier. Click T-Mobile or Use a different network.
  5. Scan the QR code.

If you already have a physical SIM active in your phone:

  1. Make sure you're connected to the internet through Wi-Fi.
  2. Swipe up on the Home screen to view your apps.
  3. Tap Settings > Network & internet.
  4. Tap the + icon next to Mobile network.
  5. Tap Don't have a SIM card? > Next.
  6. Choose your Carrier. For T-Mobile, tap Use a different network.
  7. Follow the on-screen steps to download your eSIM settings. For T-Mobile, scan the QR code.

I reached all the way to a prepaid manager (in the Philippines!) and he told me that the only solution is to factory reset the phone and activate a new eSIM the right way, then transfer the postpaid number from the old account. Problem is I spent weeks personalizing the phone and there is no way I am going to repeat that.

That is why I thought that just swapping the old SIM card to the new phone would be the simplest solution, given that all T-Mobile stores in SF are closed and the prepaid agents are atrocious. But now something is telling me that if a new eSIM card requires a factory reset, so does an old SIM card.

Anybody with knowledge about this -- help will be appreciated.