Some interesting points made, albeit from a US perspective:
But the surveillance missions in northern Mali have had only a limited effect. Islamist leaders have banned cellphones, closed Internet cafes and shut down cellular towers in an effort to cut the region off from the outside world. With the clock turned back decades, there are few electronic communications for American eavesdroppers to intercept.

General Ham said that it had been very difficult to get consistent, reliable intelligence about what he called a militant “safe haven” in Mali.

“It’s tough to penetrate...It’s tough to get access for platforms that can collect. It’s an extraordinarily tough environment for human intelligence, not just ours but the neighboring countries as well.”
Link:http://www.nytimes.com/2013/01/17/wo...agewanted=all&

I am not so sure about the mobile network being closed, yesterday several experienced reporters cited calling people in the insurgent north.