We have seen it with IM, eg. Pluggo allows people to chat in a box on your blog and you chat back using your IM, like GoogleTalk (Meebome is similar, but you chat back with your IM via the Meembo page, unlike Plugoo it’s not direct to your IM).
Anyway oTxt is similar, but for your mobile phone, that’s right, from a widget on your blog, visitors can SMS you.
Coming up is widgets to IM you from your blog (like the services above), and widgets to email you, and video message you…what about voicemail you from your blog?
[ADDED 29/12/06: Evoca : Voice comments for your blog]
[ADDED 11/01/07 : buddyPing also has a feature where people can SMS you from a widget on your blog, it also displays your location]