Your call will not connect

A call over the internet is built in three stages and can fail at any of them, which is why the symptoms differ so much. First your phone reaches our servers and says who it wants to call. Second, our carrier hands the call to the telephone network in the destination country. Third, the operator on the other end rings a handset. Only the third stage produces a ringing tone in your ear, so if you hear nothing at all, the call did not get that far.

That distinction is the fastest diagnostic you have. An immediate failure with an error message is stage one or two: the app knows the call was refused and tells you why. A long silence and then nothing is usually the network — the request left your phone and no answer came back. A ringing tone that stops means the call reached the destination and something there ended it, which is a different problem and is covered in calls that drop.

It is worth knowing that Telvio places outgoing calls only and never receives them. There is no incoming leg to misconfigure, no number assigned to you, and nothing on your account that can be in the wrong state for receiving. That removes a whole class of problems that affect apps which give you a phone number, and it also means the fault, when there is one, is on the outgoing path.

Some numbers cannot be reached from an internet calling service at all, and no amount of retrying changes it. Premium-rate and shared-cost numbers — the ranges billed at a special tariff — are blocked, because the tariff is set by the number's owner and can be arbitrarily high. Short codes, service numbers and three- or four-digit national numbers only exist inside their own country's network and have no international form to dial.

Emergency numbers are the important case. Telvio cannot call emergency services. This is not a limitation we intend to remove; an internet call carries no verified location, so an emergency operator would not know where to send help. Use your phone's own dialler, which reaches emergency services even with no credit, no SIM in some countries, and no working data connection. Our emergency calls page explains this in full, and it is worth two minutes of your time before you need it.

Numbers behind a corporate switchboard sometimes need more than the number. If a system answers and then requires an extension, dial the main number first and enter the extension with the in-call keypad once you are connected — an extension appended to the number itself with a comma or a hash is a convention some phones understand and no network does.

Voice needs very little bandwidth and is very fussy about consistency. A call uses in the region of 30 to 50 kilobits per second in each direction, which any connection made in the last fifteen years can supply; what it also needs is for those small packets to arrive steadily, and that is what public networks are worst at. A connection can measure well on a speed test and still be useless for calls, because a speed test measures how much arrives and voice cares about when.

Three specific situations account for most connection failures. Captive portals — the login page a hotel or café network shows — block everything except that page until you accept the terms, and an app trying to place a call during that window fails silently. Open the browser, load any site, complete the login, then dial. Restrictive networks at offices, universities and some hotels block the ports voice traffic uses while permitting web browsing. Networks that limit VoIP by policy exist in a number of countries, and there the block is deliberate and applies to every calling app, not just this one.

Switching between WiFi and mobile data mid-call also drops it: the call is bound to the connection it started on. If you are walking out of range of a WiFi network, turn WiFi off before you dial and let the call use mobile data all the way through. Which connection to use covers the trade-off, including how much data a call actually costs.

Write to [email protected]. A message with these four things in it can usually be answered on the first reply rather than after three rounds of questions.