It's really strange, but incredibly consistent. When I first walk into my office in the morning, for about 10-15 minutes it works just fine, I can check e-mail, send iMessages, surf the web, etc. Then about 10-15 minutes in, it just completely stops working all together for the rest of the day. At first I thought maybe something was going on in the building at a set time that causes interference to effectively shut me down (i.e., some recurring event at 8:15 AM or so), but it happens the same manner no matter what time I come in. If I come in at 7 AM it works fine for 10-15 minutes then stops, come back in from lunch it works 10-15 minutes it stops, etc.
This is exactly what happens to me. I'm fairly certain FWIF that it's due to cell phone signal boosters installed in the building. This is a guess based on 2 years of observations.
My 3G signal goes up to 5 bars when I get in the building and then cycles between 5 bars 3G and Searching all day. But the 5 bars of 3G is completely fuax, because nothing comes in or out. If I toggle 3G off, and get on the Edge network, everything works fine.
I have a suspicion that it's due to the boosters being Verizon 3G and there's some sort of interference occurring, but that's loosely based on hearsay.