It is up to you. You have the PSTN based line than you get discontinue the connection or you can send the transfer application to get the coverage. I believe that cancellation of the PSTN is more appropriate. You can get the WiFi based VoIP system to get the connection immediately. Now most of the people in USA use the WiFi system rather than the PSTN based line. In Huston you can get the connection from the local VoIP service providers.
Can you tell me, do I need to get the WiFi and PSTN line to get the coverage?
You can select the VoIP system based on the needs. Recently WiFi system is used to get the connectivity to get the coverage. It is more important to take care of the coverage on the bases of the PSTN like on the terms. WiFi system is more secure and flexible in nature to get the coverage. I think, most of the people are using the VoIP system on the bases of the terms as specified by you.
