How does your department collect phone numbers for donors/prospects? Through a subscription service or a free website?
We use a combination of free web searches and paid lists. Prospect Dev uses free searches especially when a fundraiser is struggling connecting with a prospect.
Our most common and successful tool for phone numbers has been iWave as it's pretty good at getting business contact info for us. LexisNexis is also good, but it's a lot more expensive. Otherwise, PD will see what they can find from corporate websites, Whitepages, LinkedIn, etc. to see if phone numbers or emails would be listed.
We use AlumniFinder, which you pay per lookup. Very inexpensive way to lookup addresses, emails and phone numbers.
Have you used Truthfinder or BeenVerified.com? Are these current sources for addresses and phone numbers?