Its AT&T but I sure like my Tilt (its really an HTC Kaiser) running Windows Mobile 6.0.
You can download an app called Bandswitch that gives you full control of the radios. You can make the phone use Edge exclusively when you are in bad reception areas so the phone isn't constantly trying to switch to 3G. This also greatly extends the battery capacity to several days.
My reception is much better than a friends Iphone. What a piece of junk that thing is. He can't even send/view multimedia text messages etc, has to hit some website or something to view them.