The Google Voice Blog introduces the updated version of GrandCentral that runs on Google's infrastructure including:

voicemail transcription
SMS support
conference calling
GOOG-411 integration
low cost international calling

Transcriptions
Now, in addition to being able to listen to your voicemail messages, you can choose to have your new voicemails automatically transcribed. You'll see these transcriptions in your inbox and will be able to search for voicemails. Transcriptions are also included in email and SMS notifications. They are fully automated, so they aren't perfect, but we'll be working to improve this in the future.

SMS support
When somebody sends an SMS to your Google Voice number, that SMS will be relayed to each of your forwarding cell phones and stored in your inbox. You can reply from your computer or from any of your mobile phones and the conversation will be saved in your inbox. You'll be able to read through the conversation thread and search for past messages.

Conference calling
If you want to talk to more than one person at once, just tell everyone to call you on your Google number. When you get a call waiting notification, you will have the option to press 5 to add them to your existing call.

Enjoy!