AvantiMobile (www.avantimobile.com) which also is a UK company has been offering this same service (sans the SMS feature) for almost six months now. They offer three flavors of software - Smartphone versions, which integrate transparently to the end user, so absolutely nothing is required by the user when dialing a platform call, a simple Java "dialer" version, which functions similarly to Juvino's, and a third version for more current Java devices that works both with the phonebook and as a dialer.
As a disclaimer, we developed the software for them. They're currently offering $10 worth of calling credit for new users. Rafe, I'm sure they'd be more than happy to hook you up with a nice free allowance of usage so you can try out the service first hand.
Josh @ Killer Mobile
AutoPilot - Customized greetings for every caller. One for your WIFE. One for your GIRLFRIEND.