Unlocking a 3G with somone else's SIM card

[OregonMike]

Greetings all,
I did some googling but couldn't find a sure answer.

Picked up a 3g from my little brother. Got the go-ahead from ATT to unlock with these instructions:
______________________________________________________________________
Thank you for contacting AT&T Customer Care about unlocking your iPhone.
We have reviewed your request and confirmed that you are eligible to have the requested iPhone unlocked.
Please allow 24 hours upon receipt of this notification to complete the unlock.
To complete the unlock, simply:

1. Open iTunes on your Mac or PC and verify that you have Internet connectivity.
2. Ensure a SIM card is inserted into your iPhone.
3. Connect your iPhone using the dock connector to USB cable that came with your iPhone.
4. Backup and restore your iPhone using iTunes. For information on backup and restore, please visit iTunes: Restoring iOS software.
5. After restoring, your iPhone will be unlocked.

Additional information on unlocking can be found at iPhone: About unlocking
_________________________________________________________________________________

The phone does not have a SIM card in it now. What I would like to know is: If I use somebody else's card, is that going to wipe out/mess up or cause any problem with her card or phone? Does it restore her data to my phone?

I'm going to switch over to Tmobil with the phone on their $30/month no contract plan for a bit to see if their coverage is decent in my area (Eugene, OR).

Thanks in advance for any advice!

 

[willerz2]

Shouldn't cause any troubles to their phone AFAIK as long as their line is still active. But you can immediately stick a T-Mobile SIM in there, you don't need an AT&T SIM specifically.

 

[OregonMike]

Thanks for the info. I'll swing by the T-Mobile store then & get a SIM from them & do the backup/restore to unlock it then.

Shouldn't cause any troubles to their phone AFAIK as long as their line is still active. But you can immediately stick a T-Mobile SIM in there, you don't need an AT&T SIM specifically.