Before Twitter became insanely popular, it used to allow its tweet updates via SMS message. That all stopped last August, but receiving tweets on your mobile is coming back to Twitter – at least it is if you're a Vodafone customer.
Vodafone will apparently be the only UK mobile operator to offer SMS updates for now, and will do so for free. So you can twitter to your heart's delight, from any Vodafone mobile, for nary a penny, and sending tweets from your mobile will be part of your normal text messaging bundle.
The system works with a mobile's native SMS client, using the shortcode 86444, so there's no need to install an app or use a WAP link.