Well, it is a reality today, you actually can trace mobile number without paying pay per search fees. However, there is one little problem, many internet users have either no idea that such services exist, or simply have problems finding them. And I do agree with you, as it is really hard to find something reliable and legitimate.
Personally, I have tried so many reverse lookup services, that I can't even tell how many were there. Most of them were a complete disappointment, because they either had a poor database, or they were to expensive. However, my persistence helped me find the one that is incredible, you can trace mobile number for free and there are no limitations or restrictions.
This is probably the best reverse lookup service on the Internet. The main reason I said it is because of the quality of the service they provide. You not just trace mobile number, but also they offer an access to other databases such as sex offender registry, background reports, people databases and much more. Plus, their support is extremely responsive, all my emails were answered within 3-4 hours, which I believe is very fast.
Another great thing about this service is that the member area also has lot's of information about how to protect yourself from getting traced, how to protect your information and how to find anyone you want. I can guarantee that you will be blown away by the quality of this service as it is literally the best service to trace mobile number.