iPhone: What are the differences between iPhone3GS and i pod touch 3rd as test device?

Question

I think that all iPhone developers must support from iPhone3GS to iPhone4S if your target iOS version is iOS5.
Is that correct?

So I want to test with iPhone3GS.
But it is expensive.
So I bought i pod touch 3rd instead.

What are the differences between iPhone3GS and i pod touch 3rd?
Are there problems to use i pod touch 3rd as test device as a substitute for iPhone3G?

Answer 1

One can make phone calls and connect to 3G networks and the other can't. Also, for future reference, 3rd gen will not support iOS 6 but the 3GS will (sort of). Otherwise the specs seem identical.