Which configuration works well when the client prefers to use a traditional approach to a phone syst

Which configuration works well when the client prefers to use a traditional approach to a phone system?

A.
the SPA3000 telephone adapters with an FXO gateway

B.
SPA9000 Service Model with PSTN Service only plus SPA400

C.
SPA9000 Service Model with simultaneous VoIP and PSTN services

D.
SPA9000 Service Model with VoIP Only service