The short answer
VoIP and SIP trunking replace user telephony; POTS replacement replaces analog transport for machines. Elevator phones, fire alarm DACTs, and fax need consistent loop current, battery-backed power, and supervision – properties a hosted phone system and a generic ATA do not provide.
Three different things
They are complementary, not competing. Most organizations end up with VoIP for people and managed POTS replacement for machines.
- Hosted VoIP replaces desk phones and user calling features
- SIP trunking replaces PRI or analog trunks feeding an on-premise PBX
- POTS replacement replaces the analog line feeding a single machine
Why a plain ATA is not enough
An analog telephone adapter plugged into the office network technically produces dial tone. It also depends on a switch, a router, a firewall, and an ISP circuit – none of which have battery backup, none of which are supervised for line state, and all of which get changed without telling the facilities team.
The failure mode is silence. The elevator phone stops working, nobody knows, and the discovery event is an entrapment or an inspection.
Decision table
| Line type | Right answer | Why |
|---|---|---|
| Desk phones | Hosted VoIP | Feature-rich user calling, no analog needs |
| PBX trunks | SIP trunking | Direct replacement for PRI capacity |
| Elevator phone | Managed POTS replacement | Battery backup and supervision required |
| Fire alarm DACT | Managed POTS replacement | Supervised path, central station signaling |
| Fax | Managed POTS replacement | Timing-sensitive; generic VoIP drops pages |
| Burglar/vault alarm | Managed POTS replacement | Signaling formats and path monitoring |
| Modem / dial backup | Managed POTS replacement | Needs real loop current |
What to ask any vendor
- Is the device battery backed, and for how long at full load?
- Is every line supervised, and who receives the alert?
- Which alarm signaling formats have you tested with my central station?
- Is the SIM single-carrier or multi-carrier with failover?
- Do you port numbers, and who owns them if I leave?
- What documentation do I get for inspections?
Last updated 2026-08-20.