I don't think they're accepting any new users. If you were planning on getting a free VOIP phone using Google Voice with Gizmo5, using SipGate/Sipsorcery/Google Voice can accomplish the same thing. On the phone side you can use SipDroid or Fring, I would suggest Fring as it tends to have less lag and better call quality.

Check this out: (section 8 applies to what I was describing above.)

Unlimited Free Calling with Google Voice - Google Docs

Good Luck!