Ive got the same problem now with my 32g 4S
I checked my diagnostics and there were several rests and quite a few PANIC messages there.
Phoned my service provider to be told I will have to wait 2 weeks for a replacement, till then I will have to put up with the problem.
I called my local Apple store to be told that they will not guarantee to replac it even though I am taking time out to go and see them with over an 8- mile round trip, parking and time at MY expense because their product is not working correctly.
After having all the models of Iphone since release and then passing them on to relatives and thinking of getting myself an Ipad, Im afraid the sloppiness of the 4S and the attitude from Apple has made me decide its time for change.
If Ive got to use an old fashioned phone for at least 2 weeks untill my provider gets one out to me and Apple cant guarantee they will help, Ill send it back, as its only 1 day old and give a Windows or Android a try, I can buy one of those tomorrow and Im sure they cant be as bad a this.
I cant be the only one that feels this way...