The answer is yes, TDMA voice can and has been used on commercial satellites; LEO,MEO and GEO for years. Commercial GEO satellites, for the most part, are just high powered frequency translators. All the TDMA part is generated on the ground. The complication is that all users will have a different path length and therefore a different transit time to the satellite. Compensating for this different path length is usually done by adding a timing offset to each user. For GEO satellites this is fairly simple. For orbiting satellites it must be done dynamically. It is also quite common to see VoIP transported inside TDMA frames since most current commercial TDMA modems have native Ethernet/IP interfaces.
If amateur satellite is going to make the most of digital technology, I think we will see a trend away from boxes added to analog radios and see a movement toward the method used commercially, which is have all the data handling and modulation done at a low IF frequency that feeds the appropriate up and down converters. There are many bright and talented hams doing amazing work in DSP. I would not be surprised to see a cubesat using this technology supporting numerous QSO's on a single frequency sometime in the not so distant future.
- Howie AB2S