You'll see a whole load of these temporary sites around Doha just now (and probably for some time to come!) The permanent sites are the ones surrounded by a permanent (walled or fenced) compound.

The ones on the photo are called COWs (Cell On Wheels). They're NORMALLY used to enhance coverage in a particular area or for a particular event.

They are often used by a Network Operator when a permanent site is not available ie the network is being built (as is the case with Vodafone). However, they are also used when planning permission for a permanent site is in progress or when permission is only given to install a temporary site.