Gina “Lifehacker” Trapani wrote a post about Google Voice on SmarterWare in which she says:
Now that Google Voice supports SMS, you can send and receive text messages from your GV number as well, which is the last piece I needed to finally tell all my friends and family, “Here’s my new phone number.”
She’s been using GrandCentral since it came out, and only decided to switch completely with the addition of SMS. I’m pretty sure that when I get my iPhone (cross your fingers – any day now) I’ll just tell all my friends to send their text messages to my email address. Of course, then I’ll have to make sure to keep it less than 140 characters when I write them back, but at least I won’t have to give AT&T my wife’s arm and leg to pay for a text messaging plan.