I have a working GSM handset without a SIM card. I would like to maintain it as my backup phone while travelling within the US while I am a student here.
In India, where I am a citizen, this was easy. While travelling, along with my postpaid phone (the one which I used regularly and paid a monthly bill for) I carried a prepaid card of a different carrier on another spare phone. I had the option of adding minutes to the prepaid card and the validity of these minutes was for about a year. I used to add 60 minutes to this prepaid card and that was more than sufficient for a year. My primary phone worked almost all the time and I used the backup phone only when the former's battery was dead or when it was out of coverage.
However, in the US I find pre-paid plans cost about $45/month. Maintaining a backup phone would imply maintaining a full-fledged regular phone with all its costs. What would be a good way to maintain a cheap phone (no internet, just calls) just for the sole purpose of having a backup while travelling?