Hey Vonage customers, your VoIP service of choice is about to get a bit of a mobile value-add. Announced today, the company's new Extensions service links your existing home internet calling plan to extra phone numbers -- like a cellphone-- for free, so you can make that long-distance call to Tante Lulu in Gstaad on-the-go. Okay, so the feature isn't exactly gratis -- you're still required to sign up for an unlimited international calling plan, but the bucks literally stop there. All it takes to get started with this "virtual calling card" is an access number and some foreign digits. Sound too complicated for you? Don't fret, official iPhone and Android-compatible apps are scheduled to hit their respective markets in the coming weeks. So, go ahead and ring ol' Lu for her 89th birthday. She'll be glad you called.