You could always try your old SIM from the nokia in the Dell.
The networks differ in their 3G coverage, 3 is the newest network and therefore has the least coverage. The odds are that the mast you were parked next to was for a different network (most masts are put up by a particular network and not shared). I sort of doubt that this is a phone problem.
Are you able to move between networks? (i.e., are you stuck on a contract?) If you can move, I'd suggest trying a few networks in your local area until you locate the one which gives you best coverage.