Some of the functionality that Google Voice users love like SMS notifications haven’t been carried along to the mobile web app so other developers have stepped in to fill the void.

Enter GVMax, a free web service that monitors your Google Voice account and notifies you when you receive a new SMS or voicemail.

The work around uses Google Voice’s SMS-to-email functionality using it to send the forwards to GVMax’s servers which are then rerouted to the various ways a user wishes to be notified.

When you recieve a new voicemail or SMS, the GVMax system can send you an IM, an SMS, an email or even a message on your Twitter account.

The service not only fills in a functionality gap, but it also replaces a more cumbersome hack some user were employing involving having the notifications forward to an always-on home computer running a desktop app that would then pass on the notifications to users’ mobile phones.

Nerd Vittles has a really good primer on how to connect the Google Voice client to any Asterisk system, as well as reports on progress for a Python interface for Google Voice.

Basically, with a little tweaking you can use a Google Voice account for free U.S. calling and SMS from Asterisk phone systems by leveraging a DID with free inbound calling. Nerd Vittles provides an in-depth look at the benefits of this set-up, as well as all the code necessary to make it work.

VoIP opinion blog truvoipbuzz.com takes the opposite approach in an editorial about eight reasons why you should not use Google Voice as your primary phone number. The article lists limitations in carrier networks, spotty SMS reception, and overall reliability issues as evidence that Google Voice is not a good choice for your main line.

I’m impressed by Google voice’s international rates, especially to mobile devices, but the voicemail transcription is really awful currently. I tested it several times and found about a 60 percent success rate, which left the messages largely indecipherable. I did not have problems, however, with excessive rings between connections, as some have noted. If you’ve got an account, what are your thoughts on Google Voice and its performance so far?