Glossary

What is a SIP phone?

A SIP phone is a phone that places and receives calls over an IP network using SIP (Session Initiation Protocol) for signaling, instead of connecting to a traditional phone line. It comes in two forms: hardware desk phones with an Ethernet jack, and softphones — apps that turn a computer or smartphone into the phone.

Either way, the phone registers to a SIP server (your cloud phone platform or PBX) with credentials, and from then on behaves like any extension: it rings on inbound calls, dials out, transfers, holds, and conferences.

Hardware SIP phones vs. softphones

Hardware SIP phones (Yealink, Poly, Cisco, Grandstream, Fanvil) look like classic desk phones: handset, speakerphone, programmable keys, color screens on higher models. They plug into Ethernet, usually drawing power over the cable (PoE).
Softphones are applications — the same SIP endpoint as software. Modern cloud platforms make the app the default: zero hardware cost, works anywhere, integrates screen-pop and messaging.
Hybrid reality: most businesses today run softphone-first and add hardware handsets only where a physical phone earns its desk space — reception, shared areas, warehouses.

A third option, the ATA, lets an ordinary analog phone act as a SIP endpoint — useful for keeping beloved conference phones or analog devices alive.

How a SIP phone connects

The phone is configured with the SIP server address, username, and password (enterprise fleets auto-provision this from the platform).
It registers with the server, announcing where it can be reached.
On a call, SIP handles the signaling — invite, answer, hold, transfer, hang-up — while the audio itself flows over RTP.
Features beyond basic calls (directories, presence, busy-lamp keys) come from the platform the phone registers to.

SIP phone vs. “VoIP phone”

In everyday use the terms are interchangeable — virtually every modern VoIP phone speaks SIP. Strictly, VoIP names the broad category (voice over IP, any protocol) while SIP names the specific standard that won. If a spec sheet says “VoIP phone,” it is almost certainly a SIP phone.

Common questions

Do I need a SIP phone to use a cloud phone system?

No. Cloud platforms work fully through desktop and mobile apps — the softphone is a SIP endpoint. Buy hardware handsets only for positions that genuinely want a physical phone; they coexist freely with app users on the same system. DialPhone supports both from $24/user/month.

Can I use any SIP phone with any provider?

Mostly yes — SIP is an open standard, and mainstream desk phones interoperate with mainstream platforms. Practical caveats: some carrier-branded phones ship locked to that carrier, and auto-provisioning (zero-touch setup, central management) works best with the vendor/platform combinations your provider officially supports. Check the supported-device list before bulk-buying.

What do I need to set up a SIP desk phone?

Ethernet with internet access, power (PoE switch or the phone’s power adapter), and the SIP credentials from your platform — server, username, password. On supported models, provisioning is automatic: enter a code or the platform pushes the config, and the phone comes up registered with your extension and directory.

Are hardware SIP phones obsolete?

Not obsolete — niche. Receptions, shared spaces, call-center positions with dedicated headset setups, and environments where a computer isn’t always on still justify hardware. For everyone else, the app on devices they already carry wins on cost, mobility, and features. The trend line is clearly software-first.

See DialPhone endpoints

AI business phone system → · Softphone → · Pricing →

SIP — the protocol itself
Softphone — the software form of the SIP phone
ATA — make analog phones speak SIP
SIP trunking — SIP at the carrier-connection layer
RTP — where the actual audio flows