JOHANNESBURG — Commuters can tune in while waiting for taxis thanks to Rank TV.Advertising company Comutanet has installed large screens at 10 city taxi ranks showing SABC programming beamed by satellite. Taxis in South Africa are actually buses that carry between 20 and 30 commuters and are the main transport. Trial runs have been a success, and the service is due to bow Aug. 1. Advertisers are clamoring for airtime and their chance to grab the potential 1.2 million aud. Comutanet has been trying to find a way to tap the market for some time. It tried small TV screens and radiotapes in the taxis, but both had limited success.