Replace iPhone at the Apple Store

All you can do is ask. But as modified as you say it is, I would not accept it if I was the Apple person.

Ummmm, you paid $500 for an unlocked and obviously modified iPhone and now you want to pay more money to get Apple to replace it? That's not very logical. Return it to the seller for refund, then buy one directly from Apple. That would be cheaper, right?

Regardless, Apple does offer out of warranty replacements, in the US it's $199 for the 4S and $149 for older models.

An apple retail store will replace any device that is not beyond econimal repair or a vintage or older product.

Now if your device has been opened and had components reaplced by a none authorised apple centre, this device is classed as beyond econimical repair.

Basically as long as its not been opened by unauthorised repair centres or had bits replaced by them, you should be able to do the out of warranty repair.

This is usually allowed anywhere in the world at an apple retail store, unless that specific device is location specific, eg cdma and you want reaplcement in uk, this cannot be done.

If it's been modified in the way you describe, Apple won't touch it. Try to find a 3rd party service center. You're going to have to pay for it though. You can NOT get a replacement from Apple, even out of warranty.