The absolutely free reverse phone lookup sites generally provide the most basic of information such as name and it works only for landlines. To get further information, money will have to be paid. The free searches do not provide much more than what can be found through the phone book or personal knowledge and they only want your email to send spam.
Stay away from shady reverse phone lookup sites, most likely you won't get any information after you make the payment. Not to mention you won't get a report and you won't get an answer if you try to call for a refund. Stick with a reputable reverse phone lookup site like http://phone-search.info/228/Phone-Lookups.html that has been around since 1999.
If I recall correctly they have two options:
1. $14 and you get only one report.
2. $39 and you get unlimited reports. I went with this option because I wanted to verify more numbers. This is how I caught my girlfriend cheating, I got the name, other phone number, address history, relatives, and criminal-court records.