I'm out here in Iowa City, reception and coverage are good and reliable. I'm coming from Verizon, though, so there is a drop off in service (no LTE, weaker signal).
I've yet to really go anywhere farther than the Iowa City / Coralville area, however, my roommate works in North Liberty (iPhone 4S, AT&T) and gets next to zero reception on many parts (Verizon always had me covered, everywhere); I've not been out that way yet, though I imagine both devices will grab a similar signal.
My problem with AT&T was, and likely still is, that once you really wander outside a bigger city finding a useable cell signal is hit or miss. We vacation up north (Wisconsin) where, yet again, AT&T really drops the ball but Verizon always had me covered.
There's simply no matching Verizon's network, however, 90% of the time I'm in Chicago & Iowa City, so really I only miss Verizon 10% of the time when I'm off camping, hiking, etc.
Where are you both at in IA?