When buying an iPhone, the sim you’re planning to use must be already compatible with the iPhone’s current provider setting. Most likely it’s AT&T. So if you have a Motorola GSM phone with AT&T, you can take that sim to an iPhone that’s setup for AT&T service. If you want to use another GSM provider such as T-Mobile with that iPhone, you’ll have to unlock it first by getting the code from AT&T.

Some iPhones on eBay are already unlocked by the seller, like the ones listed below, and ready for you to insert any SIM card you want to use.

• Resolved Question: What is the price of a second hand apple iphone 2g 8gb?
  if it is in good condition
• Voting Question: what is the price of an used iphone 2g 8gb?
  im getting one for rs10999 its in good condition with all accessories, is it a good deal? RS:10999(India)
• Resolved Question: how can i make an mp3 song as my ringtone on my iphone ?
  i bought 2 iphone mobiles last month 2g iphone 8GB and 3gs 16 GB and now i'm using the 2g mobile device the thing is i sync it with itunes and get the latest frimware for it and i made my liberar …
• Resolved Question: Should A 12 Year Old Get An iPhone 4?
  I'm 12 and I REALLY want an iPhone 4, I get $80 a month for allowance and the iPhone 4's plan costs $60 a month, my mom would pay for $20 she said, So that would be half my monthly allowance …
• Voting Question: Does my iPhone need a 'screen replacement' or a 'screen digitizer'?
  My iPhone screen broke and I know you can go to Ebay to buy a new one. I went to go get a new one and there are two different things to choose from. I can either get a screen replacement or a screen d …