You might try Vonage and the newer Vonage phone interface. It uses your cable internet connection. I get excellent quality patch when I use it. I do have a boost package from comcast for my internet.
There's also a Dlink DPH50U interface you can use for Skype.
I know I'm a little late on this reply....but as you know, there is nothing worse than having equipment issues when you are in a session with the client! I use the Gentner DH-20 digital Phone Hybrid (now made by Comerex, but exactly the same). More expensive, but you'll buy it once and NEVER have problems with any system. There's more to it, but I don't want to get all techy on you. Look into it...here's the link
I was able to setup a patch solution using SKYPE which works pretty well. The phone number for Skype was $30 for the year and I found instructions on plugging this into my mixer.