I would have to disagree...
The rating of any given problem is based rating of those individuals which pass of fail the puzzle. Being able to pause the trainer would allow individuals to cheat, which in turn would affect a puzzle's rating.
Perhaps a better solution might be to turn off your phone, ignore the call, or refrain from using the trainer when you are likely to be distracted.
Otherwise, accept the occassional failure due to an interuption... which is what I do.
There should be a way to put the tactics trainer timer on pause. Once you press pause, the chess board, and any analysis board that is open, should go blank.
the reason is because sometimes you are doing a tactic problem, and the phone rings. so you have to lose the problem because of this? if people really wanted to cheat that bad at tactics trainer and set up other boards to work on the answer, then so be it. but why not have a pause button that blacks out the screen until you press un-pause? i'm not that worried about my tactics trainer rating, but it would be nice
i don't know much about internet programming though, so i don't know if this is possible.