There’s a bit of buzz (particularly in the US, where AT&T is the only iPhone carrier, and they provide shitty service) around a new app called Line 2. It’s basically a whole second phone line that runs on VoIP, I think… So you can hand out your business number and your personal number and receive both calls on the same phone
http://techcrunch.com/2009/09/02/google-voice-alternative-line2-is-now-live-on-the-app-store/
