Google Calendar has had US SMS notifications since it launched, and just added UK networks to the list. I entered my details and it seems to work fine, but the initial setup message said ’standard charges apply for each reminder’ and I’ve no idea how much these would be. Standard outgoing message cost is 10p, but incoming messages can vary up to £1 (if not more). Even if it’s 10p it’d mount up over a few weeks, given how much is in my calendar. Still, it means I can theoretically add events to the calendar via SMS, which could come in handy.