Page Plus uses VZW towers.
To port, you submit all the information (regarding your current carrier). After the port is complete, you will get an e-mail with instructions on activating your phone. If you are using the same phone, then it will stop working during the port process. Then it will start back after you re-activate it.
Depending on who you are porting from, it takes anywhere from 30 minutes to 3 days. But coming from most of the major carriers (AT&T, Verizon, Sprint) it's pretty fast.