Is there a way to use listen to gsm and 3G frequencies ?

Is there any way to modify regular 3G cellphone to listen to CDMA and TDMA radio frequencies ?

I would like to know when a given cellphone is around, so I would only need to get 2 things:

• A unique identifier doesn't need to be an IMSI or IMEI, something encrypted would be ok... I just need something that doesn't change.
  
• signal strengh.

Is there a setup using wireshark to listen to the packages, some radio receiver and antenna to do that ?

Could it be done with a regular cellphone and some low level access ? is a cellphone capable of listening to other close by cellphones ?

AGAIN

I am not interested in any kind of listening to calls or getting IMEI or IMSIs. Just get the signals and list of phones in an area.

I found USRP radios and some software that could do it, but it's to expensive and complesx

Any idea is welcome.

Thanks!