I have same problem; I've done most things even the freezer temporary fix, but only lasts until phone warms up and doesn't really connect even then.
seems particular to the 4s and sees like many people are suffering the same
Apple say hardware!
I went into the O2 shop and they said software; they knew exactly what the problem was and didn't even look at my phone as they have already seen it from many other!
I feel Apple need to sort this issue?