cell phone triangulation

I'm looking to hire someone for a project to develop a cell phone triangulation system that tracks the movement of a person. I'm not sure yet what specific technological limitations or specifications I'll need, but I do need a high level of accuracy within a few meters. Someone with experience developing applications like this and who knows their way around current technology and limitations would be ideal for this job. If you think you can help me out, please let me know. I look forward to hearing from you. Thank you!

OR - if u are able to simply locate a device with just the phone number, this is ideal