well there are a number of things i would ask a service provider if i got the chance again.

1 how often does the service drop out
2 does call line quality decrease over time
3 Who do you peer with. I.e got a old boys sorry ladies for this agreement that stipulates if you call x who is with say plusnet can you call them for free and then can plusnetcall sipgate for free etc I.e no call charges like vop should be.

Long live skype