To Host or not to Host - That is the question. Since the time SIP was commercialised, there has been a religious war raging, a fierce war with two staunch opponents - On-Prem (on-site) PBXers, and Hosted (off-site) PBXers.
There are benefits to both methods, it depends on what features you want, how many channels you need (in the world of VoIP, channels = lines), and how you are going to use the system.