Short answer: They are usually not exempt and require a license.
Most countries, including, US, UK, EU, India, Pakistan, Middle East (UAE, Saudi Arabia, Kuwait), that we have studied require that a ‘banking’ license of some sort would be required by the Mobile carrier to conduct money/payments on their mobile network. In some countries, a Money Transfer Service license would suffice.
It is interesting if say a Mobile carrier “X” were to introduce MobileXCredits, which is the virtual currency that exists only on the mobile carrier’s platform, then it is a very big grey area.
Regulators in many countries (both banking regulators and mobile / communication regulators) would like to cash this opportunity via some form of a license. They play is simple, if money is deposited or cashed by a mobile carrier for goods/services to a 3rd party, the mobile carrier must be licensed to do so. Countries like India/Pakistan/Bangladesh have regulators who are fighting over this – as to whose domain it should be to license them.
Many countries still have not adequately developed a framework for this that is truly business concentric.