The phone network is one of the most under secure systems in the world. And for some reason they are not trying to hard to make it much more secure.
A recent program on this on the ABC here in Australia illustrated the ability for a really good hacker located somewhere in Romania hacked into one of our most senior ministers of parliament. He had all the conversation as well as texts etc..The minister said no way anyone could get into his phone. He was shocked after this demonstration. The prime minister could be hacked easily as we have done to our Indonesian counterparts on numerous occasions.
It was worrying.
That is why you should NEVER do any banking using your phone. You are asking for trouble. Just don't do it.