I am looking to buy an iPhone 4 from the secondary market. I currently have an iPhone 3GS. Can I just replace the sim on the new iphone with my current sim? Or is there something else that I need to do?

  • 1
    This depends on your mobile operator, best is just to ask them directly.
    – nohillside
    May 28, 2012 at 8:11

4 Answers 4


Unfortunately the iPhone 4 has a microsim card, so there is no moving your sim from pre iPhone 4 iPhones to iPhone 4. Most likely you can get one of these from your carrier.

  • So how would I tranfer my phone number and contacts? If I go to AT&T to upgarde, how would they move my data?
    – RHPT
    Apr 20, 2011 at 17:02
  • 1
    Phone number would be reassigned to a new sim, if you have your contacts on your sim card, go to settings>mail contacts and calendars>import sim contats, then sync them with a computer/mobile account. Most of the time ATT can read the contents of the sim card and put it on a flash drive, but I have seen proprietary formats in the past. Other backups stuff should go through support.apple.com/kb/HT4137 (how to backup and restore your iPhone as a new device) Apr 20, 2011 at 17:20
  • What a pain. I guess I'll skip this upgrade route for now.
    – RHPT
    Apr 20, 2011 at 18:00
  • Actually, could I just take an iPhone 4 to an AT&T store and have them move my number and such? I don't need to buy the phone from AT&T/Apple, right?
    – RHPT
    Apr 20, 2011 at 18:08
  • Usually that data transfer is when they first upgrade your phone, I havent seen them offer it to existing iPhone owners, but you could see if they would transfer them for you. Honestly the article approach is much better than letting AT&T go at it Apr 20, 2011 at 19:22

If you want to make your SIM into a compatible iPhone 4 Micro-SIM, you'll need a micro sim cutter. Look these up on ebay in your area. They're as cheap as chips and save you a ton of bother.

Look for DIY ways of making pre-iPhone 4 SIMs into iPhone 4 Micro-SIMs on YouTube. There's video instruction for how to do it yourself


Since the SIM are electrically the same, you could cut the current SIM to allow it to fit the iPhone 4 slot. Otherwise, you'll need to contact your carrier.

They will be able to assist you in ensuring the SIM cards match your account. Apple (and this forum) can help with moving the content, but only the carrier can manage the database that tracks which SIM and which phone belong on which account.

Often it's as simple as getting a new SIM card of the right physical dimensions and placing it in the device, but explaining why you want a new SIM to the carrier may speed things up.


Not sure if you have it sussed by now, but I'll give you a quick run down:-)

All of the info on the iphone is stored in the backup file you make in itunes - the iphone stores nothing on the simcard - however if you have a simcard from an old phone you can import your contacts.

So the best way is to make a backup of your 3GS in iTunes and then restore you iPhone 4 in iTunes and restore from backup - then you have exactly the same on both phones and you can erase the 3GS and continue on with the iPhone 4.

Good Luck :-)

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