There's an interesting free source of market data that I've been using for the past two years. Until two hours ago, I hadn't given this much thought, but when I mentioned it to some colleagues, their reaction was: Wow! This is really cool.
So I thought I'd share it more widely. It's Wikipedia's List of Mobile Network Operators.
There's quite a bit of information, by country and by operator, for example:
I've been tracking mobile subscriber growth for more than ten years, in part by purchasing ITU data every other year or so; in part by getting copies of any data than any NMS business unit purchases from traditional market analysts and in part by capturing anything that's published in press releases or other teasers from analyst firms.
Wikipedia doesn't have all data for all operators, but they have almost everything and it's very credible. They also cover countries that I have never seen in traditional analyst reports, for example:
Somolia is famous for having no functioning central government, no spectrum regulation and no telecom regulations, but none-the-less having the lowest international calling rates in Africa.