Best system to add phone lines for interviews on Internet Radio?

We are starting an internet radio station (non shoutcast…)While most of our programs are prerecorded, we will be doing some live phone interviews and have a call in forum… What is the best system/program to intergrate phone service into our radio service… ethernet? skype? ???? and if we are hosting a remote, what is the best system for managing say 3 lines via the internet and then mixing it back into the broadcast?

Any suggestions?