In your phone's network settings. Provided your smartphone supports the technology.
It is impossible to give one description of how to activate this on your smartphone, as the function has different names among different manufacturers. Below, however, you can see how it is activated on iPhone and a general description of where you find the setting on Android phones.
Go to Settings > Mobile Data > Mobile Data Options, and tap on Enable LTE, or go to Settings > Mobile Data, and tap on Enable LTE. If the network provider supports VoLTE (Voice over LTE), the following options will be displayed:
- Off: Turn off LTE
- Voice & Data: Allows voice calls and mobile data over LTE
- Data Only: Allows mobile data, but not voice calls via LTE
Go to the phone's settings and choose network settings. Select mobile network settings - if necessary select the right SIM card and find the setting that activates Voice over LTE. The setting can have different names and might be hidden under advanced settings.