I have an iphone 3gs, when I try to connect to my home wi-fi the phone goes thru the motions, finds the network but can't lock it in. The check mark next to the network flashes a few times then the phone goes serching again and the same thing happens.

Question

I have an Iphone 3gs wi-fi problem.  When I try to access my home wi-fi network the phone looks for the network, finds it, but cannot lock it in.  The check mark flashes a few times then the phone tries again to connect.  This only happens with my home wi-fi.  Any suggestions on how to fix this problem.  I have re-booted the phone and the router without any luck.

Answer 1

SOLUTION! 
I've been suffering from this problem for a few months.  I tried everything suggested by everyone, and then, today, I had a mad idea. 
I used to work in a room in the house that's about 12 metres away from the router. It's on the next storey up and horizontally about 8 metres away.  The problem started when I began to work in the same room as the router. 
Today I became so frustrated that for some reason I walked into a room about 8 metres away on the same level - Guess what?  I connected with no problem at all. Feeling full of joy I walked back to the room where the router is located - Dropped internet connection within a few minutes!  Walked back to the the room that's 8 metres away and, hey presto! I have a connection. I now realise that the problem was that I moved too close to the router.
I can think of no logical explanation for my experience, but empirically it seems to work.  Does anyone have the faintest idea of why this should be the case?  In the absence of an answer I think I may have to start believing in fairies at the bottom of the garden - I'm just off to set a meal for them.
By the way, I don't know if it has any significance, but the router is a BT Infinity router that has replaced the incredibly unreliable Virgin Media cable connection