Mast sharing
In line with UK government policy, it is our standard practice when searching for a site for a new base station, to see whether we can use an existing mast or structure. We also allow other operators to install their equipment on our ground based masts, where possible.
Number of O2 Base stations in service (estimate)

Some of O2 UK's ground based masts are capable of hosting equipment from other operators, but not all of these masts will meet the coverage requirements of other operators' networks. Sharing a mast means increasing the height and size of the mast and this is not always acceptable to local communities or local planning authorities, who sometimes prefer several smaller masts rather than one larger mast.
UK: www.mobilemastinfo.com
Ireland: www.comreg.ie/sector