Once the port in has been completed, your existing telephone service will immediately cease to function.
This will also mean that any services connected to the line, such as your broadband internet connection, will be disconnected.
You should check with your service provider to make certain that you're not liable for early termination fees as a result of this change.
We should also strees, that there is currently no process in place to port phone numbers for customers who are migrating to ADSL2+ Naked or similar services. You will need to make these arrangements separately.