There are several ways to track a mobile phone. Software,the most useless,reason being you need to have access to the target phone. Example. I feel like tracking my neighbours phone,he ain't gonna let me have his, her phone long enough to install software onto it. Also a virus scanner will detect it and notify you of it's existance.Another way. Hardware you can make yourself for approx u00a320 pounds. The draw back on this way is you only get one way conversation,txt. To do it properly using this way,you need a separate tracking device for EACH target phone. The best way is to use the actual networks involved. All you need for this is the IMEI. Oh i say IMEI,there is also two other ways built into mobile phones. Bluetooth,and WiFi. Both transmit serial numbers when in operation,just like your mobile transmits its serial when switched on or in use. There simply hardware addresses. And I can't say how to do that on here. Sorry it's illegal. As for changing a mobile phone IMEI,it's very easily done. The IMEI number is stored on a eeprom chip. Erasible,programmable memory chip. To do this depends upon the manufacturer make,model. You can do it with a simple code, or you may need a data cable or jig,and pc with the software on it. Companies like Nokia protect there's,you gotta be a service centre and pay for it .I.e pay for the license. Companies like Samsung,use mainly codes. Depends on the manufacturer. And the most hardest IMEI to change is iPhone s. Oh yes forgot. Cells track phones as soon as switched on,don't even need a SIM card to be tracked. Software is just snooping software,spyware. Hardware,tracking is when the phone is in use only. And a mobile device can NOT be tracked when switched off.