If they bought someone they would be forced to use them exclusively internally, as well as selling the product which they have no knack for in these times. Nortel obviously has cut their R&D back that would minimize new technology upgrades as quickly as the years before and Cienna does not have the wide range of products that SBC probably would want to use and sell to its variety of custoners.IMHO
In 1984, when the consent decree came down from Judge Green, T was in control of everything from manufacturing it's own equipment, to the research labs, to controlling the robcs, I mean everything. T only gained controlled of the rbocs during WWII for national security reasons. After the war it was never separated from the rbocs. This allowed T to offer unlimited equipment with no replacement cost to customers, you just called and they replaced everything for free. When this decree came down, T was ordered to split off Western Electric, now Lucent, which it owned and produced the equipment and ordered not to produce its equipment anymore but to open up competetion and buy from other manufacturers and give others a piece of the profit. To my knowledge, the rbocs were not given this order. As far as I know, they could purchase these entities if they so desired. I doubt they would want to do so. The rbocs are probably wiser to contract their work. I really don't know if that would be a good move or not.
OH and by the way, I managed to get to keep my old T phones, they still work great. The stuff we buy in the stores is cheap stuff that is not of good quality and doesn't last very long. My best are those old phones that were made the last.