Updating an unlocked iPhone?

I have a friend that bought an iPhone 4 on eBay and its unlocked. I'm looking to update it but don't know it it would lock him out from his carrier t moble. Any help thank you.

That depends if is factory unlocked you wouldn't have a problem, but if you are using the "gevey card" then yes just make sure that is unlocked
the only way is to go apple.com go to your account and enter the IMEI serial number it will tell you there if is lock to certain company or provider

If the phone is software unlocked, it will get locked back to it original carrier. If the phone is factory unlocked, it will not have any issues with locking.

Since it is already iPhone Factory Unlock, it won't be a problem if you update it. The Unlock will retain even if you unlock it.

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