The full picture
The real strategy for call-heavy work isn't 'walk during calls.' It's 'walk between calls and pause instantly when one starts.' That makes quick start/stop more important than walking-while-talking. The A1 Pro and X21 both handle this rhythm well. The R1 Pro is noisier due to its hybrid motor. The X25 is the loudest option and generally wrong for call-intensive schedules.
The Paceora angle
Paceora's keyboard shortcut to pause the treadmill is the call-heavy worker's best friend. One keystroke to stop before the meeting connects. No phone fumbling, no delay.