What exactly changes when I switch SIM cards on a phone?

Questions on how we spend our money and our time - consumer goods and services, home and vehicle, leisure and recreational activities
Post Reply
User avatar
Topic Author
tc101
Posts: 3210
Joined: Tue Feb 20, 2007 3:18 pm
Location: Atlanta - Retired in 2004 at age 54

What exactly changes when I switch SIM cards on a phone?

Post by tc101 » Thu Nov 14, 2019 3:47 pm

If I switch the sim cards between two phones, does anything change other than the phone numbers on the two phones?
. | The most important thing you should know about me is that I am not an expert.

runner3081
Posts: 2566
Joined: Mon Aug 22, 2016 3:22 pm

Re: What exactly changes when I switch SIM cards on a phone?

Post by runner3081 » Thu Nov 14, 2019 3:48 pm

It depends if it is GSM or CDMA.

If CDMA, not much.

Which one do you have?

Shallowpockets
Posts: 1404
Joined: Fri Nov 20, 2015 10:26 am

Re: What exactly changes when I switch SIM cards on a phone?

Post by Shallowpockets » Thu Nov 14, 2019 6:23 pm

Try it and see. Let us know. Usually you put in the sim and reboot. Sim doesn’t know what phone it’s in.

User avatar
GerryL
Posts: 2499
Joined: Fri Sep 20, 2013 11:40 pm

Re: What exactly changes when I switch SIM cards on a phone?

Post by GerryL » Thu Nov 14, 2019 7:35 pm

When I put my European SIM card into my iPhone, I have to go to a website to load some s/w that change a few settings. When I return, I have to undo the changes. That's because the SIM cards are on two different networks.

Caduceus
Posts: 2103
Joined: Mon Sep 17, 2012 1:47 am

Re: What exactly changes when I switch SIM cards on a phone?

Post by Caduceus » Thu Nov 14, 2019 8:40 pm

Are you asking if the phone provider knows that it's still you or that the second SIM card is still tied to the original phone? I've often wondered that myself.

BuddyJet
Posts: 252
Joined: Mon Jun 24, 2019 8:56 pm

Re: What exactly changes when I switch SIM cards on a phone?

Post by BuddyJet » Thu Nov 14, 2019 11:32 pm

Like others have said, it depends on the carriers involved. What are you trying to do?

Here is a basic sim explanation

https://www.lifewire.com/what-are-sim-cards-577532

bluebolt
Posts: 987
Joined: Sat Jan 14, 2017 9:01 am

Re: What exactly changes when I switch SIM cards on a phone?

Post by bluebolt » Fri Nov 15, 2019 2:01 am

As others have mentioned, it would be helpful to know a little more about what you are trying to do.

When you switch SIM cards on a phone, the phone number changes. Outgoing calls & texts will be from this new number and incoming calls/texts will be to this new number.

With smartphones, most other things won't change since they rely on a data connection that is not related to your phone number. That said, some apps that require your phone number for login or two-factor authentication will be affected. Your *new* number will need to be on your account if you want to get 2FA codes to use for login.

If you have an iPhone, it can/will also change the originating phone number for iMessage, though this will also be associated with your AppleID, so it *shouldn't* cause much of a problem. When/if you switch back, you should look at your iMessage send/receive settings and confirm they are still correct.

If you are switching to a SIM from a different country, there are potentially other impacts, like requiring a +1 in front of (US) dialed numbers where a domestic SIM card wouldn't require that.

If you are switching to a SIM from a different carrier, your previous carrier's app (e.g. the Verizon app or AT&T app) may not work on the new network from your new number.

User avatar
Topic Author
tc101
Posts: 3210
Joined: Tue Feb 20, 2007 3:18 pm
Location: Atlanta - Retired in 2004 at age 54

Re: What exactly changes when I switch SIM cards on a phone?

Post by tc101 » Fri Nov 15, 2019 2:14 pm

As others have mentioned, it would be helpful to know a little more about what you are trying to do.
What I am trying to do:

I have an android phone with AT&T with a phone number that I have had for years. It broke down a few days before I was going into surgery. I needed to get a working phone right away. I tried to switch the phone number to a new phone but I was on a group plan and the person who controlled the plan was on vacation in India so AT&T would not allow me to switch the old phone number to a new phone, or buy an unlocked phone without an AT&T plan.

I bought an unlocked android phone at Best Buy and signed up with Verizon on a month to month plan. I was able to do all of that at best buy.

When the woman who controls our group plan gets back from india I want to get out of the group plan, and get the old phone number on the new phone.
. | The most important thing you should know about me is that I am not an expert.

neilpilot
Posts: 2828
Joined: Fri Dec 04, 2015 1:46 pm
Location: Memphis area

Re: What exactly changes when I switch SIM cards on a phone?

Post by neilpilot » Fri Nov 15, 2019 2:22 pm

tc101 wrote:
Fri Nov 15, 2019 2:14 pm
As others have mentioned, it would be helpful to know a little more about what you are trying to do.
What I am trying to do:

I have an android phone with AT&T with a phone number that I have had for years. It broke down a few days before I was going into surgery. I needed to get a working phone right away. I tried to switch the phone number to a new phone but I was on a group plan and the person who controlled the plan was on vacation in India so AT&T would not allow me to switch the old phone number to a new phone, or buy an unlocked phone without an AT&T plan.

I bought an unlocked android phone at Best Buy and signed up with Verizon on a month to month plan. I was able to do all of that at best buy.

When the woman who controls our group plan gets back from india I want to get out of the group plan, and get the old phone number on the new phone.
At my Best Buy there are decent AT&T prepaid phones for $32-$40, and even one flip phone marked down to $5. They are all AT&T prepaid phones, and will work with your existing number by simply swapping sim cards. Just need to be sure the size of your existing sim card is the same as that of the replacement phone. No need for an "unlocked" phone.

smackboy1
Posts: 1133
Joined: Wed Mar 14, 2007 9:41 pm

Re: What exactly changes when I switch SIM cards on a phone?

Post by smackboy1 » Fri Nov 15, 2019 2:47 pm

tc101 wrote:
Fri Nov 15, 2019 2:14 pm
What I am trying to do:

I have an android phone with AT&T with a phone number that I have had for years. It broke down a few days before I was going into surgery. I needed to get a working phone right away. I tried to switch the phone number to a new phone but I was on a group plan and the person who controlled the plan was on vacation in India so AT&T would not allow me to switch the old phone number to a new phone, or buy an unlocked phone without an AT&T plan.

I bought an unlocked android phone at Best Buy and signed up with Verizon on a month to month plan. I was able to do all of that at best buy.

When the woman who controls our group plan gets back from india I want to get out of the group plan, and get the old phone number on the new phone.
SIM = Subscriber Identity Module

SIM chip identifies you to the cellular network. A cell phone is basically a 2 way radio and the AT&T SIM contains information that identifies you as a valid account holder with AT&T and it's partner's networks so your phone # works and you get service. If you swap your SIM chip to a working AT&T phone or an SIM unlocked GSM phone, the new phone will have access to your AT&T account and your phone # and should work. However AT&T is a GSM carrier and Verizon is CDMA. Even though both companies' phones use SIM chips, they are not compatible. It's unlikely that and AT&T SIM will work on an unlocked Verizon phone.

For a GSM phone to work on a network the hardware has to be compatible i.e. it has the correct radio frequencies. Also the phone has to be set to use the proper APN (Access Point Name). Sometimes a SIM will automatically set the phone with the proper APN, sometimes it has to be done manually.

However, what you are looking for is to take your phone # out of the group plan. That has nothing to do with the SIM. What the group plan owner will have to do is allow you to port out your phone # to your own plan. If you stay with AT&T it's simple because AT&T is already provisioning your #. They just have to establish the old # with a new account under your name. If you want to port your old # to a different cell carrier, like Verizon, it's more complicated. You have to go to the new carrier and establish a new account, then your new carrier has to initiate a port out. Essentially the new carrier requests a transfer of the old phone # from AT&T.

No matter how you do it, when you establish your new account with a new phone, they will give you a new SIM to go with your new account and new phone.
Disclaimer: nothing written here should be taken as legal advice, but I did stay at a Holiday Inn Express last night.

User avatar
Topic Author
tc101
Posts: 3210
Joined: Tue Feb 20, 2007 3:18 pm
Location: Atlanta - Retired in 2004 at age 54

Re: What exactly changes when I switch SIM cards on a phone?

Post by tc101 » Fri Nov 15, 2019 3:42 pm

I think it will be easier to just stay with AT&T as you describe. I will give the verizon phone to a friend.
. | The most important thing you should know about me is that I am not an expert.

Post Reply