3G wasn't designed to be forward-compatible. It expects to have a dedicated frequency band it can operate on. But spectrum is limited, and telcos really don't want to reserve something like 25% of what little spectrum they have to support a handful of legacy devices.
4G/5G support Dynamic Spectrum Sharing. This means a single frequency can be used to carry both technologies, with the ratio between them adjustable as demand varies. With DSS a 5G base station reserving a tiny fraction of transmission time for legacy 4G emergency calls would be absolutely trivial, which makes future hard shutdowns unnecessary from a technical POV.
3G wasn't designed to be forward-compatible. It expects to have a dedicated frequency band it can operate on. But spectrum is limited, and telcos really don't want to reserve something like 25% of what little spectrum they have to support a handful of legacy devices.
4G/5G support Dynamic Spectrum Sharing. This means a single frequency can be used to carry both technologies, with the ratio between them adjustable as demand varies. With DSS a 5G base station reserving a tiny fraction of transmission time for legacy 4G emergency calls would be absolutely trivial, which makes future hard shutdowns unnecessary from a technical POV.