VoLTE, short for Voice over LTE, carries your phone calls over the same 4G data network that handles your browsing, instead of routing them through an older 2G or 3G voice circuit. Because the call travels as data, it connects faster, sounds clearer (carriers market this as HD Voice), and lets you stay on 4G while talking rather than dropping down to a slower network. On 4G/LTE networks that have switched off their legacy voice bands, VoLTE is the only way calls work at all.
This matters when you travel with a data eSIM. Most travel eSIMs are data-only: they give you internet, not a local phone number, so your calls and texts still ride on your home SIM. In a dual SIM setup that means the travel eSIM handles data while your primary line stays reachable for calls. For that home line to actually ring abroad, its VoLTE has to be switched on, since many networks now retire the old circuits it would otherwise fall back to. If VoLTE is off, you can end up with fast data and a phone that never rings.
Turning it on is quick. On an iPhone, open Settings, then Cellular, pick the line, tap Voice and Data, and enable VoLTE; Android hides a similar toggle under the network or SIM settings. Do this before you fly, confirm your handset supports it on our device compatibility page, and if you would rather route calls over the internet entirely, read about wifi calling. For a full walkthrough of getting your data eSIM live, see our guide on how to install and activate an eSIM.