WiFi calling works without cell phone reception, WiFi alone is enough:

[https://www.swisscom.ch/de/about/news/2015/08/20150827-MM-Bessere-Empfangsqualitaet-mit-WiFi-Calling.html] (https://www.swisscom.ch/de/about/news/2015/08/20150827-MM-Bessere-Empfangsqualitaet-mit-WiFi-Calling.html)

I’ve experienced it myself…

---

@Schitzaumpie10 wrote:

Do you have one on the waffle?

---

Keep the ball nice and flat and follow the [rules of conduct](https://community.swisscom.ch/t5/So-l%C3%A4uft-apos-s-hier/Behaltensregelen-und-funktionen-der-Community/td- p/566832).

That’s why WiFi calling is there, even if there is no cell phone reception. There is no need for at least one line of cell phone reception. At least you can easily test it yourself with Android devices. Switch on airplane mode and then activate the WLAN. Calls also work perfectly, provided of course there is reasonably good WiFi reception.

I thought SMS didn’t work over WiFi calling.

For all services in the mobile network, there is now a solution to handle this service via an IP network, such as 4G/LTE, 5G or WLAN/WiFi. For SMS, this solution is called “SMS over IMS”. The most important services for the mobile phone in the IP network are:

- VoLTE (Voice over LTE) -> Voice telephony over 4G/LTE mobile network https://de.wikipedia.org/wiki/VoLTE

- VoWLAN (Voice over WLAN), also called VoWiFi (Voice over WiFi) or “WiFi Calling” -> Voice telephony via WLAN/WiFi

- “SMS over IMS” also called “SMS over IP” (SMSoIP) -> SMS over IP network (4G/LTE, 5G or WLAN/WiFi)

Whether this service is supported over an IP network depends on the mobile phone, the mobile network and the SIM card. See post no. 7 at:

[https://community.swisscom.ch/t5/Mobile/4G-VoLTE-telefonieren-mit-externer-antenna-oder-analogem-telefon/m-p/638087#M8203] (https://community.swisscom.ch/t5/Mobile/4G-VoLTE-telefonieren-mit-externer-Antenne-oder-analogem-telefon/m-p/638087#M8203)

For all of these services, the user data is transmitted exclusively as IP data packets. All of these services require a functioning IMS (see post #22).

VoWLAN enables voice telephony via the foreign holiday hotel WLAN/WiFi if the data traffic is routed through a VPN tunnel over the home Internet connection. VoWLAN is only possible with the mobile phone provider Swisscom if a public, Swiss IPv4 address is used!

For technical details about the VPN tunnel see post no. 1065 at:

[https://community.swisscom.ch/t5/Mobile/Advanced-Calling-VoLTE-und-WiFi-Calling/m-p/533122/highlight/true#M4663] (https://community.swisscom.ch/t5/Mobile/Advanced-Calling-VoLTE-und-WiFi-Calling/m-p/533122/highlight/true#M4663)

If you have problems with VoWLAN, see article no. 14 under:

[https://community.swisscom.ch/t5/Mobile/WiFi-Calling-unzuverl%C3%A4ssig-Gem%C3%A4ss-Swisscom-Support-nicht/m-p/580976#M6378] (https://community.swisscom.ch/t5/Mobile/WiFi-Calling-unzuverl%C3%A4ssig-Gem%C3%A4ss-Swisscom-Support-nicht/m-p/580976#M6378)

and post no. 10 at:

[https://community.swisscom.ch/t5/Mobile/Wifi-Calling-scheint-nicht-zu-funktionieren/m-p/662173#M8888](https://community.swisscom.ch/t5/Mobile/Wifi- Calling-doesn’t-seem-to-work/m-p/662173#M8888)

For information on radiation exposure when using VoWLAN, see article no. 11:

[https://community.swisscom.ch/t5/Mobile/WiFi-Calling-unzuverl%C3%A4ssig-Gem%C3%A4ss-Swisscom-Support-nicht/m-p/523044#M4238] (https://community.swisscom.ch/t5/Mobile/WiFi-Calling-unzuverl%C3%A4ssig-Gem%C3%A4ss-Swisscom-Support-nicht/m-p/523044#M4238)

In general, the use of VoWLAN/VoWifi is not recommended. See “Good Performance Rule” no. 10 and No. 22 under:

[https://community.upc.ch/d/4397-diagnose-tool-der-connect-box-says-your-home-network-hat-derzeit-einige-probl/27](https://community. upc.ch/d/4397-diagnose-tool-der-connect-box-says-your-home-network-has-currently-some-probl/27)

It is better to use a “Dual SIM” capable mobile phone with a cheap “roaming SIM card” such as the (no longer available) Swiss Mobile SIM card when abroad.

https://swiss-mobile.swiss.com/myaccount/rates?l=de

In Switzerland, the use of “Dual SIM” capable mobile phones is generally recommended:

[https://community.swisscom.ch/t5/Mobile/2G-Abschaltung-2020-neue-weisse-Flecken-kein-Empfang/m-p/617825#M7418] (https://community.swisscom.ch/t5/Mobile/2G-Abschaltung-2020-neue-weisse-Flecken-kein-Empfang/m-p/617825#M7418)

For use within Europe, the use of a “Natel FL” SIM card could also make sense (Swisscom Abo for Liechtenstein):

[https://www.swisscom.ch/de/privatkunden/abos-tarife/mobile/abo-uebersicht/natel-abo-in-liechtenstein.html](https://www.swisscom.ch/de/privatkunden/ abos-tarife/mobile/abo-uebersicht/natel-abo-in-liechtenstein.html)

On the topic of “VoLTE roaming” see:

https://community.swisscom.ch/t5/Mobile/VoLTE-Roaming/m-p/657972

In my opinion, SMS can also be used via WiFi calling. What I would try (at least it works with Android phones): Put the phone in airplane mode, then only activate WiFi. Then 3G/4G is switched off, the device stays on WIFI and doesn’t switch. This way you can also test whether SMS are arriving, whether calls are being made, etc.

Simply turn off airplane mode when you leave the house, otherwise you won’t be reachable. But you usually notice it relatively quickly 🙂

@Explorador

If there is no tick mark from the mobile network at all for Wi-Fi calling, normal SMS does not work on the cell phone. We have already had a few cases with users who did not receive an SMS during telebanking and, for example, Had to move outside to get the code via SMS via mobile network.

Yes, then I can’t help either. I just tested it: Samsung set it to airplane mode, then activated WLAN again. I’m only connected to WiFi now. Can make calls, receive SMS. In my opinion, the device is no longer connected to the mobile network, so no problem.

What kind of special SMS the bank sends that needs an anchor in the mobile network… I have no idea.

---

@Explorador wrote:

What kind of special SMS the bank is sending that needs an anchor in the mobile network… I have no idea.

---

SMS are tied to the mobile telephone network at a very low level. This cannot work with a pure IP connection.

https://de.wikipedia.org/wiki/Short_Message_Service#Technik

The bank may also offer other two-factor authentication (Cronto Sign)

@Anonymous

At least 3GPP disagrees with you. SMS is also available via LTE and WiFi. Just because the service has been around for a long time does not mean that it is low level. Wikipedia writes about SMS via landline, which was abolished because there were few to no users.

https://www.3gpp.org/news-events/1268-Dispelling-LTE-Myths

@Explorador

Danke für die Quelle! - Nur bitte - wo siehst du hier, dass es auch über WLAN geht? (LTE ist immer noch Mobilnetz!)

Myth 2: SMS isn’t supported over LTE

Reality: LTE and EPS will support a rich variety of messaging applications and also SMS is supported over LTE. The solution is twofold, covering both the full IMS case and a transition solution for those networks that do not support IMS.

SMS over IP was fully specified 3GPP Rel 7. It depends on IMS and it is intended to provide compatibility between the existing cellular legacy and the implementations with more elaborate messaging capabilities via SMS and IMS interworking..

For environments without IMS a transition solution was specified. This is called SMS over SGs (previously called the misleading name: SMS over CS). It is a hybrid approach that allows the transmission of native SMS from CS infrastructure over the LTE radio network. SMS over SGs was specified as part of Rel 8. SMS over SGs provides SMS service for mobiles in LTE and since it requires also CS domain infrastructure for the SMS transmission, it is intended to be a transition solution.

---

Anyone who can read has an advantage: “SMS over IP” aka “SMS over IMS” works in every IP network (-> Post No. 20). Regardless of whether the mobile phone is connected to an IP network via 4G/LTE, 5G, WLAN/WiFi, or any Ethernet network connection via a USB-C adapter (-> Post No. 15).

---

@GrandDixence I suspect that the blame lies with the manufacturers and their implementation of WiFi Calling:

On my cell phone, for example, “Wi-Fi telephony” can be activated, but there is only the fixed setting “Mobile radio preferred”.

That’s why it only works for me if I also deactivate the mobile network via flight mode.

This is how it works perfectly: I can make calls and send and receive text messages via WLAN with WLAN telephony activated and the mobile network deactivated at the same time (airplane mode).

Thank you again for your detailed explanations, I learned a lot!

---

@Anonymous wrote:

@GrandDixence I suspect that the fault lies with the manufacturers and their implementation of WiFi Calling:

On my cell phone, for example, “Wi-Fi telephony” can be activated, but there is only the fixed setting “Mobile radio preferred”.

Therefore, this only works for me if I also deactivate the mobile network via flight mode.

---

Then the dog is more likely to be buried with the end customer:

According to article no. 15, the use of “WiFi calling” is not recommended. That’s why cell phone manufacturers correctly set the fixed “mobile radio preferred” setting. As long as mobile phone reception is available, this should be used for voice telephony thanks to the better-functioning QoS mechanisms. “WiFi calling” should only be used if there is no longer any mobile phone reception or the end customer forces the use of “WiFi calling” via “airplane mode and then switching on WiFi” due to unreliable mobile phone reception.

“WiFi calling” is and remains an emergency solution!

WiFi calling is suitable, for example, for voice telephony in a basement where there is no cell phone reception and you don’t want to or can’t use a landline phone.