I am in the process of transitioning to Google Voice, although there are a lot more challenges than you may expect because the companies in the industry just can't play nice and let the consumer chose how to configure their services.

Like many, the rejection of the iPhone app by Apple has was a real disappointment for me. Not having this makes initiating calls from the iPhone with my GV number as the caller identifier hard.  This issue and the poor AT&T network performance of late make the switch to the Droid and Verizon a real possibility even though I still have a while to go on my AT&T lock-in.

Another challenge has been getting the right "behavior" when calls are received.  I have calls routed to my mobile and to my office desktop (through a Skype In number). Unfortunately, the Skype In service does not really let you shut off its own integrated voice mail service.  There are workarounds like leaving call presentation on in GV,  forwarding to a "dead" number or getting your sequences to extend beyond 25 seconds, but all have drawbacks.  Skype In also has the issue of requiring to add duplicate contact records to your Skype contact list to get correct caller identification when someone calls.

Google has its own deficiencies.  It won't let you tie your GV service to a Google Apps account, so it has to be tied to your personal Google account.  Same issue that still exists with iGoogle, Reader and Google Profiles.  This is specially hard for me since Google doesn't seem to recycle unused GMail names so I have never been able to get johfleming or johncharlesfleming which are the personal ids I use on all other services.  The GV transcription service is a really nice feature, but has a long way to go in reliably transcribing messages.

I haven't decide dyet whether GV will replace my Skype To Go service. The lack of an easy speed dial facility is a real stopper here.  I also haven't tested GV international call quality, although the rates seem to be inline with everyone else.

All this being said, I will probably continue the transition.  The capabilities of GV to deliver voice and text messages to your inbox, to be able to effectively archive and search for them and to have unique greetings for callers really do improve voice communications. Theer are some nice third party tools coming to market like this Adobe Air desktop client that was recommended  by Kevin Purdy at LIfehacker.   It is a really nice addition.

So how about you?  Are you using GV?