This one's for UK users, but probably for some other countries too.

I'm with O2 for my phone in the UK, which doesn't support email to SMS gateways (not for free at least!) so I thought I was out of luck in terms of getting SMS reminders (which are awesome).

However, O2 DOES give free SMS updates from Twitter. Set up the RTM Twitter service, then Direct Message (DM) RTM with "!on" to enable reminders. Then enable your mobile on Twitter. As part of the RTM setup you'll be following "RTM", and you need to enable mobile updates from them within Twitter.

Once that's done, RTM will DM your Twitter account when your tasks are due, then Twitter will SMS you! As a bonus, if you need SMS updates because you don't have a smartphone, you then gain the ability to add tasks to RTM by sending an SMS to Twitter - check out http://www.rememberthemilk.com/services/twitter/ for a list of what you can do!

Oh, Twitter also emails you when you receive a DM - I just filter for subject "Direct message from Remember The Milk" straight into the trash, but that's up to you.