How to set up a SIP app: Linphone, Groundwire, Zoiper

What a SIP app does

SIP is the standard protocol behind internet telephony. A SIP app registers with your provider using a username and a password, rings when someone calls your number, and places your outgoing calls through the provider. Unlike a browser tab, it can ring when your screen is off — if it is set up for it.

On Numonym, every number and every extension has its own SIP credentials and a QR code that configures an app in one scan. You can connect several apps and devices to the same number: they all ring together, alongside the browser.

Which app to choose

App	Platforms	Price	Good to know
Linphone	Android, iOS, desktop	Free, open source	Can import an account from a QR code; popular with privacy-minded users
Groundwire	iOS, Android	Paid	Push notifications, so calls can ring while the app is closed
Zoiper	Android, iOS, desktop	Free, with a paid upgrade	Simple interface, widely used

On an iPhone, choose an app with push notifications if incoming calls must ring reliably: iOS stops background connections quickly. On Android — and especially on phones without Google services, such as GrapheneOS — an app that keeps its own background connection is the safer choice; Linphone can run as a foreground service for exactly this.

Connect with a QR code

1. In your Numonym account, open the number (or the extension) and choose Connect a SIP app. A QR code appears.
2. In the app, look for the option to add an account from a QR code or from a remote configuration:
   • Linphone: in the account assistant, choose to fetch a remote configuration, then scan the code.
   • Groundwire: add a new account and use the QR code option.
   • Zoiper: use the QR code option when adding an account if your version offers it; otherwise enter the settings by hand.
3. Scan the code. The account appears with a “registered” or green status.
4. Place a test call to make sure you can hear and be heard.

Menu names change from one version to the next. If you can’t find the QR option, the manual method below always works.

Enter the settings by hand

Every SIP app asks for the same few fields. Copy them from the SIP page of your number or extension:

Each SIP password belongs to one number or extension. If a device is lost, change that password from your account: the other devices keep working.

Two optional settings improve call quality. Put Opus first in the codec list, then G.722 and G.711 as fallbacks: Opus adapts to weak connections, while G.711 is understood by every system. And if your app offers ICE or a STUN server, enable it — it helps the audio find its way through home routers.

Fix common problems

• “Registration failed”. Check the username, the password and the server for typos, and make sure the transport matches the port (TLS with the TLS port).
• The phone doesn’t ring when the app is closed. The app needs push notifications or a background connection. Check its notification and battery settings — battery savers often stop SIP apps.
• One-way audio or no audio. This is usually a network or router issue. Enable ICE or STUN in the app’s network settings, or try mobile data instead of Wi-Fi.
• Choppy sound. Choose the Opus codec if the app offers it; it copes best with weak connections.
• Echo. Use headphones, or enable echo cancellation in the audio settings.
• Calls drop after about 30 seconds. The network is losing track of the call, usually because of a router or a firewall. Switching to TLS often solves it; otherwise enable the app’s keep-alive option.
• Menu keys don’t work when you call a company’s phone menu. Set the DTMF mode to RFC 2833 (also called RFC 4733 or “RTP events”), which is the standard way to send keypresses.

If calls must reach you no matter what, add a fallback: forward calls to another phone after a few seconds, or let voicemail take them — the transcription reaches you wherever you like, including Telegram or email.

Beyond one phone

For a team, the phone system gives each person an extension with its own SIP credentials — as many as you need, with no per-seat pricing — and desk phones can be provisioned automatically. Each extension can have its own caller ID, voicemail and spending limit.

Already running your own PBX, such as 3CX, FreePBX or Asterisk? Connect it with SIP trunking instead of individual apps.