General considerations
The Opis 60s/PushMeFon mobiles currently (as of 2021) use quad-band 2G network technology. This means that they can operate on any 2G network worldwide. However, in some countries some network operators have discontinued 2G service.
There are currently two further network technologies in operation around the world: 3G and 4G (the latter also known as LTE). We are not contemplating a switch to 3G technology as in many cases network operators tend to view it as a stopgap technology between 2G and 4G (LTE) and 3G service will be switched off before or at least at the same time as 2G service in most of the countries affected.
We are in the process of developing a 4G (LTE) telephony platform for our products. The problems with a direct switch to this technology are that while the 4G network has been available worldwide for some time, there are significant differences from region to region. In particular no agreement could be found on a solution that allows one LTE device to participate in voice communication everywhere in the world. The voice call technology for 4G (LTE) is called Voice over LTE (or VoLTE for short), and, sadly, it hasn't been standardised, which means that several different implementations need to be used at the same time in order to allow global 4G (LTE) technology voice coverage. In addition 4G also needs to work on more than 70 frequency bands compared to 4 frequency bands for 2G. The combination of these factors has meant that 4G phones were either restricted to one global region or very expensive. It is only starting in 2020/2021 that affordable 4G VoLTE technology ICs will be available on which we can base our mobile telephony platform in the future.
In summary, currently our quad-band 2G network still offers the best option for cost-effective coverage in most countries, but we are actively developing 4G (LTE) and Voice over LTE devices and will switch over to the technology once this becomes viable. We expect this to be the case in 2022.
Specific Country Information
Valid as of June 2021 to the best of our knowlegde (please also see: https://en.wikipedia.org/wiki/2G)
(If in doubt, please ask your network provider if they can provide a SIM-card for 2G. We can assume no responsibility for the correctness of this information.)
Australia
Compatible 2G networks include: Telstra (Christmas Islands only). All other networks (including Telstra on the mainland) are not 2G compatible.
Canada
Rogers has postponed their 2G shutdown a second time. Now it is scheduled for the end of 2021 (Please check with a representative if you can still register a new 2G phone on the network to run until the end of 2021). All other 2G networks are shut down.
China
China Unicom has started to shut down their 2G network in some regions and plan to complete the shutdown by the end of 2021. All other operators still support 2G.
India
All networks are 2G compatible, except JIO/Reliance.
Japan
There are no compatible 2G networks.
Macau
There are no compatible 2G networks.
Mexico
Movistar (and Virgin Mobile, QBO Cel, weex, Cierto, Maz Tiempo, Flash Mobile) and AT&T have shut down their 2G networks. Telcel (and Qui Móvil) continues to support 2G.
Netherlands
T-Mobile (and Tele 2 - which uses T-Mobile's network) have shut down their 2G network. KPN and Vodafone continue to support 2G.
New Zealand
Compatible 2G networks include: Vodafone
Singapore
There are no compatible 2G networks.
South Korea
There are no compatible 2G networks.
Switzerland
Sunrise will support 2G till at least end of 2022. All other networks are not 2G compatible.
Taiwan
There are no compatible 2G networks.
Thailand
There are no compatible 2G networks.
Trinidad and Tobago
Digicel, Flow support 2G.
UK
2G is compatible with all networks, except iD Mobile.
USA
T-Mobile continues to provide 2G service to the end of 2022 and will perform a full-switch off then. Sprint continues to offer limited 2G coverage till the end of 2021.
All other countries
Service should be available via the mainstream network operators. (Some speciality network operators - notably 3/Three - may surcharge for use of a 2G service or block it. It is best either to avoid them or to find out the exact conditions beforehand.)