Last night on BBC radio, I heard about an interesting innovation called WhatsApp, which you can think of as Skype for SMS delivered as a smartphone app.

Traditional SMS uses the carrier voice network, allowing carriers to charge for SMS as they would for a phone call and sometimes leading to compatibility issues between carriers. WhatsApp uses the data network instead of the voice network, letting you send text and MMS without paying normal carrier SMS charges (the BBC story reported a charge of a $1 per year for WhatsApp after the first year, which is free). If you have a smartphone, check out the FAQs on the WhatsApp website.