Google Voice is now offering instant invites for those in the military. All Google requires is a .mil address, be in the US and have a phone in the US. Their expediting invites within a business day or two. Here’s a quote straight from Google:
It is hard enough to keep in touch with family and friends, but imagine being half-way around the world in a place like Iraq with limited access to telephones…or having to move and change your phone number every couple years. The military lifestyle often presents unique communication challenges that Google Voice can make easier, so we are giving priority invites (sent within a day) to active military and reserves with .mil email addresses at: www.google.com/militaryinvite.