South Africa is one of Research In Motion’s (RIMM) top five markets in the world, and it is a decent proxy for the entire African market. Leading regional carrier Vodacom’s November smartphone statistics illustrate exactly why BlackBerry 10 cannot arrive soon enough… and why RIM badly needs a cheap new BlackBerry 10 model by spring.

Vodacom holds more than 50% of the South African handset market and South Africa is the largest mobile phone market in the continent.

On November 12th, Vodacom announced that it had 2.7 million BlackBerry users on its South African network, a number that increased by 300,000 in three months. The number of Android users grew by 200,000 to 700,000 subscribers. The number of iPhone users grew by 250,000 to 500,000.

Of course, there are many ways at looking at these trends but it’s striking that the growth of the BlackBerry user base has slowed down to 12% in a quarter while Android growth is now at 40% and iPhone growth is 100%. Even though the pool of BlackBerry users is still expanding in the most important African market, we are now close to the tip-off point where the absolute number of both Android and iPhone users added each quarter is going to be larger than the number of new BlackBerry subs.

RIM announced last week that its global customer base has finally started shrinking — the BlackBerry subscriber pool dropped from 80 million to 79 million between the August and November quarters.

During the August quarter, RIM still managed to add 2 million BlackBerry subscribers. The non-U.S. BlackBerry subscriber base is still growing, but too slowly to offset the U.S. erosion. This is the trend that the Vodacom November numbers also reflect. In Africa and Asia, that BlackBerry growth slowdown is unlikely to reverse until RIM launches a cheap, sub-$250 model with the new BlackBerry 10 OS.

In South Africa, affluent buyers are now flocking under the iPhone banner, while Samsung (005930) and Chinese vendors are mopping up middle class consumers with cheap Android models. New high-end phones in the $600 range are not going to change this equation.

RIM must strike hard in the low-end market to regain its African momentum. By Easter, Android and iPhone camps will have pulled ahead of RIM in new subscriber additions at Vodacom. Next spring, South Africa could well be the most important global bellwether of RIM’s struggle to recapture subscriber growth.