Travel as in overseas, or within the US?
If the former, having an unlocked phone and just getting a prepaid SIM card at the destination is a popular solution.
Since you don't use seem to use your cellphone very much, a high end device like the Nokia N8
($400) is probably overkill. Shame, cause it's probably one of the best travel phones around. Carrier unlocked, quad band GSM and pentaband 3G antennas, free lifetime GPS with turn by turn navigation and worldwide offline maps, great camera for snapshots/travelblogging and ultra long standby battery life. I just got a topographic GPS app for outdoor activities as well.
If you're confining yourself to the US, AT&T has a $2 unlimited daily plan
where you only get charged on days you use the phone (I'm assuming that you'll continue to not use the phone when you're at home).
Wind, Sand and Stars.