[ian0]

It depends on the country but typically there is a set of central bank regulations which attempt to ensure adequate safeguards are in place when non-banks offer banking services. Example protection of the float for stored value wallets and enforcement of anti-money laundering KYC for peer to peer transfer.

Central banks also tend to (sometimes sensibly) clamp down on services that are closer to core (profitable? :P) banking services like interest & loans, so telco wallets with this functionality built in house are much rarer.