Would a T-mobile SIM card work with an unlocked iPhone that's on the iOS 4?

[soniak]

I'm debating whether or not to buy an unlocked iPhone off craigslist that have been updated to the iPhone 4 OS - I hear that the new one isn't compatible with T-Mobile and such. Is this true? Detailed opinions and feedback very much welcome. Also, I'm looking for it to work on the iPhone 3GS specifically. And I know T-Mobile has great options I could go with, but I have the first generation iPhone and I love it, I'm just looking for an upgrade

[Unregistered]

A T-mobile SIM card will definitely work with an iPhone if the device is unlocked in a safe method. So, ensure it from the seller before buying the device. Certain unsafe unlocking methods would give iOS problem while working with other SIM cards. Temporary unlocking methods will also relock the iPhone on your future iOS updates. Resulting in more expense. So it is better to buy a network locked iPhone for low cost and unlock it safer and permanently by yourself. You can unlock an iPhone using remote unlocking service. You can get the remote unlocking service for an iPhone from MobileUnlockSolutions.com This method of unlocking is safe, simple, affordable, quick and permanent. It doesn't require a jailbreak too. Good luck.