I sometimes have a problem with my 3GS I can be texting or surfing the web and I will lose service or data some times both when I'm in a area that has perfict coverage is this a iPhone issue or a tower problem??
the first thing you do is power down. then try again.
the second thing you do is call tech support from another phone.
they need to cancel your location e.g. flicking the network switch.
after power down cancel location and power up then your data should work again.