I want to suggest you the most simple way to promote a pay per call campaign:
Track your traffic and make sure that you attract the right customer
Always make sure to make your site look legit and creative
Use different marketing channels to promote your business
Try to know your customer and use important data to drive your marketing
Be in continuous contact with your account manager.
If you are running pay per call campaigns or working with inbound calls, Ringba gives you everything you need to setup, track, manage and optimize your call marketing campaigns so you can generate higher-quality calls and more conversions for your buyers.
Here are just some of the things
Ringba allows you to do with Pay Per Call:
Get Tracking Numbers
Route Calls to Targets
Manage Call Campaigns
Create Custom IVRs (beta)
Attribute Traffic Sources Analyze Reports
I hope this helps you!