It is of course possible to verify the given phone number by calling it, but this usually annoys people. There is much better solution for it which you can implement in your company's IT system. You can find at least a few companies which allow you to lookup phone numbers automatically using their API, so that you don't have to perform each and every check manually. This will save you a lot of time and effort. For sure there will be some records which have to be verified by a human, but most of address and phone numbers data can be checked automatically.
Even if still don't see any practical use of phone lookups in your company, consider the following situation. The only information which possess about your customers are names and phone numbers. Not much if you would like to send a Christmas card. However, you could always call your customers and ask them for addresses to send the cards. On the other hand, as I mentioned before such solution will not be consider comfortable for your customers and will generate additional costs. When using reverse phone lookups automatically, you will be able to append an address to each of the phone numbers. It is no difference if it's a cell phone or a land line. Good service providers have databases covering all of these phone numbers.
The last thing which can prevent you from implementing such system in you company might be the cost of developing it. Try to ask your IT office for the cost of such operation and believe me, you will be surprised that it's so low. Usually these are just a few hours of programmer's work but when you imagine the advantages you will quickly realise that it's definitely worth it.