I was asking myself the same question about a week ago and the answer IS Google Voice.
I bought an invite from eBay for $1.35. It's just a little bit of a hassle to use but it's not a big deal at all.
If you want your friends to text you, they will have to text your Google number NOT the number provided by the carrier. So just have your friends store one number for Mobile, and the other for Text, not that hard =P.
The other thing is how to get notified that you have received a text. As of now, the Google Voice refresh rate or something is like 2min, meaning it will check to see if you have received a text every 2min. Google is currently aware of this and is working on fixing it.
However, there is a simple fix around it: check the option that says it will send an email to your Gmail when you have received a text. And this has no delay (the 2min refresh rate), and you will be instantly notified when you get a text through your Gmail. The only downside of this is that your mail will be flooded with 'SMS from xxxxx.' You can't use Gmail options to label and send to certain folders as you will not be notified if you do this.
But all in all, it's an amazing alternative. I was extremely impressed even with the slight disadvantage.
Good luck!