If you work for a phone network, you would probably know that if the government can't monitor your phone than your phone is not allowed to operate in that country. This is pretty much law in every country. This is why there was such a fuss recently with blackberry messages. Blackberry now must relay all text messages to a government server like the rest of the networks. FBI for example are able to track you and enable the mic to listen in on most phones today.
It is for 'security purposes' and has/is being used to monitor terrorist etc, but there has also been reports of personnel abusing their powers.