Here are a handful of places that I visited in Morocco that have better voice coverage on a GSM network than my home in San Francisco. You can argue that the cityscapes are flatter and waves may be better able to penetrate clay than the building materials used at home. You could argue that in an area as flat as the Sahara desert, it's not surprising that you get great coverage because there is little to nothing that can interfere with a signal. It was still astonishing to me how good the coverage was in those areas.
The top criteria for consumers when selecting a carrier are quality of coverage at home and while traveling.
Tannery in Fez
Abdul on his cell phone in the High Atlas Mountains
It's hard to see, but there is a cell tower in this town in the distance.
Sahara near M'Hamid
Sand dunes near M'Hamid
A Kasbah near Ouarzazate
Habib's camel sleeping after a long walk