I think that we can't send pictures (MMS) through google voice, only text (SMS). I have 2 cell phones (one for work, one personal) so I've been doing a lot of testing.. and... I figured something out.
You can use Gmail to "email" a cell phone. So, I sent a gmail to the number which looked like firstname.lastname@example.org and attached a picture. It worked.
Alltel: phone email@example.com
AT&T for SMS firstname.lastname@example.org, for MMS email@example.com
Nextel: firstname.lastname@example.orgT-Mobile: email@example.com
Verizon: for SMS: firstname.lastname@example.org, for MMS: email@example.com
Virgin Mobile: firstname.lastname@example.org
US Cellular: phone email@example.com (SMS) phone firstname.lastname@example.org (MMS)
Nice, eh? Its a bit of work, using Gmail AND having to know their network.. but it works. Well, the tests I ran worked. If anyone else can check, try it out.
Anyone know if Google voice plans to support MMS eventually?