How much would it cost to upgrade my iphone 3GS to an iphone 4s?

How much would it cost to upgrade my iphone 3GS to an iphone 4s?

It depends. If you are due for an upgrade, not a lot. If you aren't. It's like $300 or something. Assuming you have ATT, log into your account and click "upgrade options". I suspect Verizon may have something similar, but I'm not sure.

Why are you asking us instead of your carrier?

Depends what carrier you have.

Straigh out cost? Or are you eligible for an upgrade? $99 if eligible to upgrade, if your not eligible then the full price of the phone.