Something I've done instead is use an unlocked SIM phone and buy SIM cards of countries as I passed.

India is a little awkward in that regard. Telecom is cheap, but paperwork/requirements were toughened after Mumbai bombings and there can be differences in how well different phones work in different states. However, if you can make it work and buy SIM cards as you go along and use text messages to a twitter account - then it can be easy to check in occasionally. I was in India earlier this year for six weeks (not cycle touring, though I did bring a mountain bike for city riding) and a local cell phone worked well.

I found other countries easier to get SIM cards and some even selling them in airports or standard places. I also found even when no going to the largest cities, that cell service is pretty broad. I'd still set the family expectations that sometimes no message means you are in area with no service, but otherwise normal cell service and text messages would be an alternative to consider.