About the credit check, we'll mine isn't perfect but it didn't seem to bother 3.
I ordered everything online and less than 24hrs later the iPhone was on my doorstep.
I would suggest sticking with it until sept next year, as no doubt there will be a new iPhone or other super smart device about to be released, then choose an upgrade and sell your 4s.
What's your network coverage like (what area are you in?) as I'm in Scotland and at times I get poor signal (In my house for instance).
All the best though