It's the policy of carriers to credit the accounts of customers when fraud is detected. Besides, you'd be amazed at the technology a cellular carrier can bring to bear to aid your investigation. It may be possible for the carrier to develop a suspect, even down to his name and address, by analyzing the call detail. There's a computer record of every call made, you know. Also remember that cellular phones are simply two-way radios.
Some carriers have the hardware to do radio direction finding from cell sites.
They can actually triangulate and pinpoint the position of a fraudulent caller. Sometines they may simply diagnose signal strength to determine the distance to a caller. The industry is developing new methods of trapping and tracing cellular calls. But they can't do it alone, and neither can you. It is the marriage of the company's technology with the skills of the detective that make an effective team.