My new 6820 phone cannot play MIDI files that have drum track (midi channel 10). It just reports "can't open file". Some of midi files with simple drum track could get played on the phone but most of midi files couldn't get. I've tried to cut whole drum track or shrink it to few seconds and got that midi files played. This problem is permanent and depends only on drum track.
I've saw same problem on 7250 phone year earlier but thought that because only 4-voices polyphony on 7250. But the 6820 has 16 voices and should play almost all midi files without problem. Btw, i see on the forums another report about "can't open midi file" error. Perhaps, this problem affects whole series 40?