For something specialized like Asterisk, I'd definitely recommend talking to your prospective host before signing up to make sure that things will work with their system. As the previous poster said, GoDaddy doesn't specialize in VPSs - I'd suggest looking at someone who does that might have done something similar in the past.

Some recommendations that we've had good luck with are Linode, VPSLink, VPSLand and ServerAxis.