I've got an old Nokia 3310 phone which I've had for nearly 8 years. I don't use it as my main mobile any more (not since December 2004), but after I got a new phone I unlocked it and enabled the Network Monitor functions. The unlocking was through a serial port cable which goes to a special connector underneath the battery.
The Network Monitor screens show lots of data about the phone's battery, software and radio transceiver. The best ones are tests 3,4,5,11 and 17. The current channel number and Cell ID are shown, as well as the channel and signal strength of nearby cells. Signal strengths are in dBm, how can a cheap mobile phone display signal strengths in 1dB steps but on the amateur bands we still have to have meters in S-units which may or may not be about 6dB per unit except when we're using FM?
Other phones often have some kind of Network Monitor screen (there's an Android app which can show the Cell ID but not the channel number, at least on my HTC Hero). On my Sony Ericcson K750 I could get Cell ID and channel numbers on a built in test screen.
The most interesting test of all is number 17, BTS Test. This locks the phone to a single radio channel, so it can't look for the nearest base station. The channel number is selected by storing it as a phone number at address book position 33 on the SIM card.
You can go up a hill and get a base station far away (over 50km), as long as there is nothing local on that channel. At home in an upstairs room I can get the Vodafone base station at Lancaster (the same site as the GB3LD repeater), which is on channel 77 (950.4 MHz).
The base stations are identified by the country code, network number, LAC and CID. LAC is the region of the country where the station is. This helps give a rough idea of where an unknown base station might be if there are none nearby.
For Vodafone, the LAC in this local area is 170.
The CID is the Cell ID. It could be used more than once in the UK, but with a different LAC. Different networks have different CID numbering systems. O2 has the most meaningful.
For O2, the CID is usually a 5 digit number.
The first digit is the sector (the direction of the base station antenna, where there are usually 3 different antennas on separate frequencies, spaced at 120 degrees round the mast). The sector number is 1, 2 or 3.
If the CID is less than 5 digits for an O2 site, an omnidirectional antenna is being used or only a single panel. This might be because it's an old site which has been around from the analogue days or it only has to cover a small area like inside a tunnel.
Sector numbers usually go clockwise starting with 1 as the most northerly pointing antenna. So a CID of 15432 would be base station 5432, beaming north. 30439 would be base station 439, probably beaming towards the south-west. If this was simply CID 439, it would probably be an old site with a single omnidirectional antenna.
If the last 4 digits are 0001 to 01499 then there's a good chance the site had been used for the analogue cellular system, but not always, some newer sites use numbers in that range.
Some older Vodafone cells use a similar numbering system but with the sector number at the end. If the last digit is zero then it is omnidirectional. Newer sites don't follow this system and the numbers mean nothing.
The Lancaster Langthwaite site I get at home has a CID of 1643. This is an old site, which was in use for analogue phones. On the Sitefinder website, this is shows as being site number 164. I'm roughly west of Lancaster, so sector number 3 will be mostly directed towards Barrow.
At the railway station in Barrow there is a Vodafone site with 2 omnidirectional antennas. This is site 3753 on Sitefinder and the CID is 37530.
Channel numbers on the 900 MHz band (O2, Vodafone) are 0.2 MHz offsets from 935 MHz. So channel 75 is 950 MHz.
O2 normally use 37 - 59 and 101 - 124.
Vodafone normally use 65 - 99
On the UK networks, only the odd channel numbers are widely used, except for channels 123 and 124 (for some reason channel 123 is missed out and 124 used instead).
At 1800 MHz, T-Mobile are using the channel 575 - 715 range and Orange in the 750 - 870 range, but that might change now it's the same company.
Some local sites:
CID 10439, channel 109 (North)
CID 20439, channel 101 (towards Ulverston)
CID 30439, channel 57 (towards Barrow)
Lancaster TV mast
CID 10210, channel 53
CID 20210, channel 55
CID 30210, channel 124
CID 2930, channel 91
CID 1643, channel 77
2 other sectors unknown channel numbers
Dalton TV mast
CID 8334, channel 65 (Dalton town centre)
CID 8335, channel 93 (south-west)
CID 8336, channel 97 (north)
All except Dalton TV mast used to be analogue sites.
Old analogue control data channels:
Morecambe Bay Vodafone = 935.8375 (omni)
Morecambe Bay Cellnet = 943.5125 (omni)
Langthwaite Vodafone = 935.6875 (sector 1), 935.8625 (sector 2), 936.0375 (sector 3)
Lancaster TV mast Vodafone = 935.7375 (omni)
Lancaster TV mast Cellnet = 943.0875 (omni)