Here is what Wikipedia say about retention of phone records:
Telephony Data - retention period 12 months All numbers (or other identifiers e.g. name@bt) associated with call (e.g. physical/presentational/network Assigned CLI, DNI, IMSI, IMEI, exchange/divert numbers)
Date and time of start of call Duration of call/date and time of end of call Type of call (if available) Location data at start and/or end of call, in form of lat/long reference. Cell site data from time cell ceases to be used.
IMSI/MSISDN/IMEI mappings. For GPRS & 3G, date and time of connection, IMSI, IP address assigned. Mobile data exchanged with foreign operators; IMSI & MSISDN, sets of GSM triples, sets of 3G quintuples, global titles of equipment communicating with or about the subscriber.
In addition it has been reported that the UK police and security services have the following additional capabilities on mobile telephones, provided by telephone operators, but not covered by the voluntary code.
- The capability to record to the content of selected conversations.
- The capability to determine the location[6] of a mobile telephone to within a few yards by using triangulation and multiple base stations.
- The capability to remotely activate the microphones of some mobile
telephones.
The UK Financial Times of the 2nd August 2005 [page 4 of the UK edition] reported that the UK police can ask mobile phone operators to download special spying software to a mobile telephone without the user’s knowledge or permission.
When this has been done the authorities can turn on the microphone of a mobile telephone and listen to any conversations in its vicinity. This capability only exists for mobile telephones which can accept downloaded software. The telephone must be turned on for the microphone to be activated, but the user does not have to be making a call.
http://en.wikipedia.org/wiki/Telecommunications_data_retention