Sounds like it could be a few things, personally I'd do a speed test just to make sure you're still getting a good connection, you can find one at dslreports.com or if you want a voip-targeted one, www.vonage-forum.com has one. It might be that your cable modem supports only docsis 1 when your ISP might have moved over to docsis 2 as well.

Finally, it could also be that you're not forwarding required ports to the packet8 box.. If your packet8 box happens to do QoS (where it would have an "out" port for ethernet devices, then perhaps it needs to be plugged into the modem first. *shrug*

Sorry I'm kinda feeling funky right now, hope this stuff helps