This tower supports cellular and PCS antennas on the top platform, replacing the microwave antennas that were once located there.Like the Riverton tower shown above, this tower is a four-leg square skeletal structure built by AT&T's Long Lines department for long distance voice service. In recent years, AT&T has removed many of its intercity microwave links from service, and replaced them with fiber optic links. In the process, it has removed microwave antennas from the towers, and, in many cases, recycled the towers for other purposes. Here we have an example of a recycled tower. It's a far stronger structure than cellular and PCS antennas would require, but it certainly serves the purpose.
Of course, AT&T isn't the only long distance company that has replaced microwave links with fiber. Frequency congestion in the microwave bands has made it practically impossible for any company to add new capacity to existing microwave links, so fiber has turned out to be the only way to add network capacity. Here's an article that I wrote a few years ago on this subject.