There are two temporary windows in portability, the Administrative and the Window of change. During the Administrative window, which is usually the most extensive, between 7 and 15 days, you continue using your line normally.
During the Change Window, technical procedures are executed to change operator, and these can cause the line to be unavailable, for a short period of time, which should not exceed a few hours.
Normally the Window of change is made in a low or no activity schedule and probably you will not appreciate it. The only symptom is that once the change is finished, you will start receiving faxes in your eComFax service.