Lots of helpful pay per call info posted here by RingPartnerMike and I was about to sign up, but a google search turns up lots of comment spam accusing them of fraud and some comments claiming non-payment.

http://answers.yahoo.com/question/in...0034841AAwV07Q
http://www.affiliatevote.com/ring-partner/
http://www.affiliatefix.com/f54/ringpartner-5426/
Obviously that is far from conclusive but it's enough to raise an eyebrow, anyone worked with them and can vouch for them?
If you are interested in running PayPerCall offers, check out Mobile Fused which is a niche network with years of experience with PayPerCall offers.
You should sign up 
These negative posts started showing up after we suspended a publisher for fraudulent activity. We never actually said we weren't going to pay out, we just asked for a compliance call to discuss their traffic and call quality. Not sure why they have it out for us, but they have posted all over the place, bad-mouthing us.
RingPartner was founded by myself, Ryan Gerhardt and Todd Dunlop. I headed up the SEM team at Neverblue and started my own network, Qwik Media. Ryan also worked at Neverblue and built Neverblue Mobile. Todd was one of the original founders of Neverblue.
So, we are legit and we pay our bills 
Sign up here - https://switchboard.ringpartner.com/signup/
You can add me on Skype - RingPartnerMike, email me at mike@ringpartner.com, or call/text me at 1.250.686.8956.
PS: We'll be at ASW14, Meet Market table #804. Stop by and say hi.
They're good people, you have nothing to worry about.