What is the source of this information? There are loads of hoaxes about all sorts of things, this sounds like one to me although I haven't been able to find any reference to it as either a hoax or scam.  I've never heard of any way of controlling a phone by calling it with a number, I've heard of many hoaxes though. Just check out http://www.hoax-slayer.com and you'll find loads of them.

Many companies such as Securitas Direct, Caja Madrid and other banks that have a central number call from numbers that you can't call back on, invariably long numbers that start with a 6. Next time I'm called I'll take note of the length and number.

Nigel