Is this like grasshopper? I don't think I get how this is different.
Actually that's a a fair question. Unlike Grasshopper, Google Voice, Skype, and the other similar services SimpleVox lets you both setup "virtual" phone service where calls are transferred to external phone numbers, and "native VoIP" where you can use your SIP credentials on on softphone or IP deskphone. Unlike other PBX's SimpleVox knows that modern companies and startups work differently, so you can use it both as a traditional PBX, a Google Voice clone, free conference bridge, and anything in between.
Awesome stuff. Keep up the good work. Looking at the interface now and I'm impressed. Can you transfer an existing Google Voice number to your service?