Zoiper is the softphone most people reach for first, because it runs on everything and the free tier is enough to place calls. It is also the softphone that most often gets blamed for problems that are actually a codec mismatch or a NAT setting three menus deep. This guide covers the configuration that works and the four settings that account for most failed setups.

What you need before you start

Four things from your provider, and no more:

  • SIP domain or server address — a hostname or IP, sometimes with a port
  • Username (sometimes called the authentication user or account ID)
  • Password
  • The codec the route expects — usually G.711 ulaw or alaw

If you have been given an outbound proxy address, keep it; you will need it in the advanced settings. If you have been given an IP-authenticated trunk instead of credentials, Zoiper is the wrong tool — IP authentication belongs on a PBX with a static public address, not on a laptop.

Adding the account

Install Zoiper 5 from the official site rather than an app-store clone, then:

  1. Open Settings → Accounts → Add account.
  2. Choose Yes when asked whether you already have an account.
  3. Enter your username and password, then Login.
  4. When prompted for a host, enter the SIP domain your provider gave you.
  5. Let Zoiper run its protocol probe. It will test SIP UDP, TCP and TLS in turn and select the first that answers.

If the probe finds nothing, the account details are right but something is blocking signalling — skip to the troubleshooting section rather than retyping the password a fourth time.

Pin the codec instead of negotiating

This is the single most valuable change you can make, and it is not the default.

Open Settings → Accounts → your account → Codecs. Zoiper ships with a long list enabled and negotiates whichever the far end prefers. On an international route that usually means the call ends up transcoded, which adds processing delay and costs you audio quality on every leg.

Remove everything except the codec your route actually uses. For most termination that is G.711 u-law in North America and G.711 a-law elsewhere. Add G.729 only if your provider told you the route is G.729 and your bandwidth is genuinely constrained.

A pinned codec also makes failures honest: if the call fails outright rather than sounding bad, you know immediately that the far end expected something different.

Dial in E.164 format

Enter numbers as country code followed by the national number, with no local trunk prefix, no spaces and no brackets. A UK mobile written locally as 07700 900123 is dialled as 447700900123. Some platforms want a leading +; confirm which during testing rather than assuming.

If you are used to dialling 00 or 011 for international, stop. Those are national trunk prefixes, and passing them to a SIP trunk usually produces an invalid-number rejection that looks like a routing failure.

The four settings that cause most problems

Network settings and STUN

Under Settings → Network, Zoiper has STUN enabled by default and that is usually correct on a home or office connection. Leave it on. Turn it off only if your provider explicitly tells you their SBC handles NAT and STUN is interfering.

Registration expiry behind aggressive routers

Some consumer routers close the UDP mapping faster than the registration refreshes, so the phone shows registered but incoming calls never arrive. Lower the registration expiry to 120 seconds under the account's advanced settings, or enable keep-alives.

SIP ALG on the router

If audio is one-way or registration drops every few minutes, SIP ALG on the router is the first suspect. Many consumer implementations rewrite SIP headers incorrectly. Disabling it is a standard controlled test, not a universal rule — change it alone and re-test so you know whether it was the cause. The full diagnostic order is in the one-way audio guide.

Power management on laptops and phones

Zoiper on a sleeping laptop or a battery-optimised Android will miss inbound calls and drop registration. Exclude Zoiper from battery optimisation on Android, and stop the network adapter from sleeping on Windows.

Testing before you trust it

Place calls to several valid numbers on different networks in your destination, and check each of the following deliberately:

  • Audio in both directions, not just yours
  • Whether keypad tones reach an IVR — DTMF fails silently more often than speech does
  • Post-dial delay: how long between the last digit and ringback
  • What happens on busy, invalid and unanswered numbers
  • Whether the duration and charge in your call records match the call you actually made

A route that works on three calls to one operator has not been tested. The method for doing it properly is in comparing route quality.

When Zoiper is the wrong choice

Zoiper is a single-user softphone. If you are running a team, put a PBX in front of it so extensions, queues and reporting live in one place. If you are running outbound campaigns, you want a dialer rather than agents dialling by hand — see dialer modes. And if you need consistent audio at a fixed desk all day, a hardware IP phone is more reliable than any laptop softphone, for the reasons set out in softphone, IP phone or ATA.