How to create a hunt or hunt like (rollover, multi-line) grp

I have about 5 incoming USA SIP lines, but my provider does not have any sort of roll-over or huntgroup feature. Does anybody have an idea on how I can create a general number that will ring to the next available, non-busy SIP line that I have? Is there a provider out there that would do this?

Any suggestions would be greatly welcome.

Thank you.

i guess you have 5 seperate lines with 5 diffrent numbers and only 1 call possible at each number?