I used the phonepak for about 8 years in various A2000/A3000D/T and A4000. At one point I had 4 lines running.
I found it does not like AdIDE and trumpcard did not work well in the A2000.
A3000D/T needed the rev 11 buster if you did not have 16 bit fast ram.
A4000 worked with 3.1 rev 040 board IF the screen saver was running. It seemed to add enough DMA delay to make it work. Otherwise the audio would be choppy. The screen saver was that spliner or splinter (sp?) screen saver that came with OS3
