Why an 0800 number won't connect from a mobile phone when it works from a landline
When the company's 0800 (toll-free) number answers from the office landline but won't connect from a mobile phone, the problem is almost never the answering side. It sits somewhere between the caller's carrier and the number's configuration. This article lists the causes in the order worth checking them.
Summary
- An 0800 call is free for the caller; the subscriber pays, and a call from a mobile phone usually costs the subscriber more.
- Many 0800 services let the subscriber choose which origins the number accepts calls from; a forgotten restriction knocks out mobile calls.
- Each origin follows its own route to the 0800: one route can fail while the others work.
- Test from at least two mobile phones on different carriers, and write down the time, the calling number and what you heard.
- For telecom providers, Anatel requires the phone support line to take calls from both landlines and mobile phones.
Why does the 0800 work from a landline but not from a mobile phone?
Because a call from each origin takes a different path to the 0800, and it only takes one of those paths failing. A call from a mobile phone goes through the caller’s mobile carrier, which has to hand it to the carrier that owns the 0800, which translates the 0800 into the real answering number and only then delivers the call to the company’s trunk and IVR. An origin restriction, a misconfigured route or a translation set up for only some origins knocks out mobile calls without touching landline calls.
What are the most common causes?
| Cause | What a mobile caller hears | Where to check |
|---|---|---|
| Origin restriction on the 0800 service | A carrier announcement saying the call cannot be completed, or a busy signal | The 0800 contract and configuration with the carrier that owns the number |
| 0800 translation set up only for some origins or areas | A number-does-not-exist announcement, or silence | The carrier that owns the 0800 |
| A faulty route between the mobile carrier and the 0800 carrier | Silence, or the call drops after a few seconds | The caller’s mobile carrier and the 0800 carrier |
| The trunk or IVR rejects the format of the calling number | A busy signal, or an error message from the PBX itself | Inbound rules on the PBX or SBC (A-number format) |
| Trunk capacity exhausted at peak hours | Busy at certain times | Contracted concurrent channels and trunk occupancy |
Origin restriction
An 0800 call is free for the caller: under Anatel’s numbering regulation, the subscribing organization pays for the call. Since a mobile call usually costs the subscriber more, many 0800 services let it choose which origins the number accepts calls from. A restriction set up to save money, or inherited from an old contract, makes the number work from a landline and fail from a mobile phone. It is the first thing to ask the carrier.
Translation and routing
Behind every 0800 there is a real number. The carrier that owns the 0800 holds that translation and can configure it by origin or by region, for example to send each state’s calls to a different support center. If the translation for mobile calls, or for one region, is wrong or missing, only those calls fail. The same happens when the route between the caller’s mobile carrier and the 0800 carrier has an interconnection problem.
The PBX or SBC itself
Calls reach the company’s trunk carrying the caller’s number, and that number comes in different formats depending on the origin: with or without the leading 0 and the carrier selection code, with the area code, sometimes in international format. An inbound rule that accepts only one format, or that uses the calling number to pick the destination, can reject mobile calls. In the PBX log they show up as rejected, for example with SIP 403 or SIP 484.
How do I test before opening a ticket?
Place test calls from several origins at the same time and write down the result of each one.
- Call from a landline and from mobile phones on at least two different carriers, within the same 10 to 15 minute window.
- For each call, write down the calling number, the carrier, the time with its time zone and what you heard: a normal answer, silence, a busy signal, a carrier announcement (copy the wording).
- Check the PBX or SBC log for the calls that should have arrived. If there is no record, the call never reached your trunk and the problem is upstream, at the carrier. If there is a record with a rejection, the problem is in your inbound rule.
- Open the ticket with the carrier that owns the 0800, attaching the table of calls. Ask it to check the origin restriction and the number translation.
What do the rules require of the support line?
For SACs (the customer-service channels Brazilian law regulates) in regulated sectors, Decree No. 11,034/2022 (Decreto nº 11.034/2022) guarantees free access to the SAC and makes phone support mandatory. For telecom providers, Anatel’s General Consumer Rights Regulation, Anatel Resolution No. 765/2023 (RGC), is explicit: phone support must be free, available 24 hours a day and take calls placed from landlines and from mobile phones. An 0800 that won’t connect from mobile phones leaves out exactly the customer who only has a mobile phone.
What about monitoring?
Monitoring with real calls shows whether the 0800 connects and whether the IVR answers with the right message, from the origin it calls from. Monitor calls from the 2N5 platform: it alerts you when the number stops connecting or the IVR changes, but it does not test each mobile carrier. For a restriction that only affects mobile phones, the manual test above is still the way to go. See how 0800 and IVR monitoring works.
Frequently asked questions
Is calling an 0800 number from a mobile phone free?
Yes. Under Anatel's numbering regulation, on the 0800 code the subscribing organization takes responsibility for payment, and the call is free for the caller, from a landline or a mobile phone. That is why the cost of a mobile call falls on the company that owns the number.
Why do some companies block mobile calls to their 0800?
Because a mobile call to an 0800 costs more for whoever pays, which is the company. Some 0800 contracts let the subscriber choose which origins to accept. A restriction set up to save money, or inherited from an old contract, keeps customers who only have a mobile phone from getting through.
How do I prove to the carrier that the 0800 doesn't connect from mobile phones?
Place test calls from mobile phones on at least two carriers and from a landline, at the same time. For each one, write down the calling number, the time with its time zone and what you heard: silence, a carrier announcement, a busy signal. With that, the carrier can find the route that failed.
Does monitoring that calls the 0800 catch this problem?
It does when the failure affects the origin it calls from. Monitor calls from the 2N5 platform, so it shows whether the 0800 connects and whether the IVR answers with the right message from that origin. It does not replace testing from each mobile carrier.