Here is the ultimate spy gadget. Key in up to 20 cellular phone numbers that you would like to monitor, and when there is an in coming or out-going call made to or from the number you have specified, the unit will intercept the conversation and display the number of the phone being used
You can also do general monitoring, with a push of a button, the unit will scan, intercept and display the number of the phone that was picked up
This can connects to any tape recorder, and you can automatically record both sides of all conversations. This works with all mobile phones. This is also time setting and DTMF output enabled, and you will have a date and time stamp for each conversation.
The only setback is the price -- this unit costs a cool $2,950
More details available at the vendor's site at: