I met with Marc Fribush at ITEXPO and we discussed their hosted Asterisk offering. I met Marc previously at TMC Days, when several VoIP and telecom companies visited TMC's offices. It's an impressive product. In about 60s you can "spin up" your very own virtualized hosted copy of Asterisk. Tomorrow, at ITEXPO they're announcing whitelabeling for resellers. One interesting pricing model for Aretta is that they sell per concurrent SIP channel instead of per user. So for example, if you have 72 users but only need a T1 worth of SIP channels (24), you'd pay $40 x 24 channels as opposed to $40 x 72 users, which is 3X the monthly cost. This reminds me of a post I did earlier today about Ringio on InPhonex where it was $40 per user.
Here's a quick video of Marc Fribush explaining their hosted Asterisk solution: