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