I'm doing the same -- will cancel my iPhone service as soon as the unlocking is done. I use very few voice minutes in a month and since I almost always have my iPad along as well, I'm just going with the iPad month-to-month data service, and a PAYG plan for voice (T-Mobile). I also have a Virgin Mobile MiFi with the WalMart option for 1G for $20 if I need to use my laptop.

My non-smartphone of choice is Motorola Razr. Fairly small and light plus accessories available. The one I have a bought used a couple years ago for European trips.