If I buy an unlocked iPhone, will I still be able to use wifi and all the features?

Only if you have a data plan set for your current phone. For example, if you have a Sidekick with a data plan, it would work.

You should still be able to use the wi-fi and most of the features. Visual Voicemail™ is an AT&T-only feature.

where would you buy an unlocked iPhone

eBay

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BTW, an unlocked/jailbroken iPhone is typically restorable to original locked/in-jail operation, should the need arise.

@Hollister, are you being sarcastic? Have you heard of this place called eBay?

As long as it’s unlocked properly, everything will work (apart from Visual Voicemail as rob already said).

Everything works perfectly on mine.

Yes you will, but you will not have the proper data plan.

and what is the data plan for?

To access the Internet outside of wifi.

I have a data plan on a non iPhone tarriff, surely there are similar options available to you.

Why not just buy a regular iPhone and unlock it yourself? If you’re able to follow a guide at the “1. Take off your shoes. 2. Take off your socks.” level, you’ll be fine.

I don’t have an iPhone myself—I want the 3G one—but I’ve unlocked one for a friend of mine. I was amazed that she didn’t try to do it herself when I discovered how insanely easy and quick it actually was.

its the same if i buy it unlocked or not, I want it because I have an AT&T pay as you go, so I think I can use it either unlocked or not, I only use my cell to send text messages and picture messages in Mexico and USA, I will use it with mi AT&T sim card anyway.