Some really old geezers could probably give you more details, and it has been touched on above, but I think some further explanation is in order.
Prior to 1988, or thereabouts, all the SWC schools (Arkansas may have gotten out a little before then) sold their football radio rights as a package deal, and for several decades, the rights to these broadcasts were owned by Humble/Esso/Exxon (for simplicity, we'll just say Humble). When Humble had the network (until about 1977), the games were broadcast without commercial intterruption, other than the announcers reading a commercial for Humble intermittently throughout the broadcast. Each school had their own set up for basketball, but by combining the rights for football, you only need four stations in a market to carry the games and cover all the conference action (at least when it was an 8 team league and they were all playing conference games). Humble also got the big stations to broadcast games, unlike today when its a rarity.
Humble maintained a staff of announcers much like the TV networks do now: In the '50s, if Kern Tipps was calling your game, you knew that it was the marquee game of the day--in the early '70s, Connie Alexander was the lead guy. Legends like Frank Fallon and Jack Dale, who were the basketball voices of Baylor and Tech, respectively, might be sent to broadcast an A&M-Rice game, or what have you. Dave South was one of the last guys to join the old Humble (then Exxon) network.
About 1977, Exxon gave up this arrangement, and the rights were sold to Mutual, who maintained the same system for a few years. Then, in the early '80s, mostly to placate the Horns, they began to assign announcers to specific teams, with the home team announcer doing play-by-play, and the visiting team announcer doing color. If you've downloaded the highlight clip of the '86 A&M-Baylor game, you will hear a much more neutral Dave South doing play by play with an occassional color comment from Frank Fallon. It wasn't until '85 or '86 that Dave South actually became the A&M announcer (Dave was working in Waco all the time previous to this).
Finally, in '88 or thereabouts, the schools set up their own football broadcasts, and thus ended the legacy of the old Humble network, leaving us with the every man for himself approach that is utilized today (and which probably makes sense now that we're in a different conference).
Final note: Some poster above mentioned Dewayne Staats. Dewayne never broadcast Aggie football--while he was in this part of the country, working for the Astros, Mutual ran the SWC radio broadcasts and Dewayne was committed to baseball through September. However, his offseason job for several years, and during Shelby Metcalf's greatest days, was calling A&M basketball. Back then, our games were broadcast on KRLD in Dallas and WOAI in San Antonio, both clear channel stations that could be heard throught the state at night.
[This message has been edited by twk (edited 5/7/2003 8:59a).]