Like Google Voice, Ribbit Mobile is a sort of virtual receptionist: It can ring multiple phones at once, gives you Web-based access to voicemail, and can transcribe messages into text and alert you via e-mail or SMS. But Ribbit works with the phone number you already have (Google Voice recently introduced a no-new-number option, but it’s missing lots of features).
Other stuff that’s interesting about Ribbit Mobile: It has a “Caller ID 2.0” feature that integrates your address book with feeds from sources like Twitter, Facebook, and LinkedIn in order to show you stuff about the people who have called you. It provides embeddable widgets that let people call you from within blogs, Facebook, and other sites. It lets you opt for premium services from third-party companies (such as those who do voicemail transcription with humans, not just machines). And unlike Google Voice, it’s an open platform, so other companies may build apps and services that connect to it and incorporate its features.