There are many ways to integrate a pay per call campaign within your current traffic sources. The lead quality is, normally, a lot higher of quality than that of a simple lead submission form. This allows for higher payouts and new insights to be available for the publisher. If you haven't given it shot yet, I'd recommend starting with a pay per call campaign and try both WAP ads and web landing pages. I have a few running myself internally and it's definitely something to look in to.