It is relatively easy to intercept conversations on mobile telephones. Scanning devices can be bought from retail electronic shops.
Unlike fixed telephones, which can be intercepted only fixing a physical tap on the receiver (unless the tapper has access to telephone exchanges), mobile phones can be intercepted using scanners, which depending on the sophistication of the particular scanner are more or less are limited in range and the frequencies it can intercept. Long distance calls using microwave bands can be tapped by computer equipment. Senior civil servants and others in sensitive government jobs are usually warned about the vulnerability of mobile phones to interception.
Eavesdropping mobile phone conversations in the UK is not illegal, although unauthorized publication of the information is as a result of copyright in the spoken word if recorded. Either party to the tapes of recorded conversations in 1991 of the Prince and Princess of Wales could have applied for an injunction to stop publication (but to do so would have involved admitting the tapes were genuine).