Ours runs on Viva, on 5G. Armenia has three operators, Viva, Ucom and Team, and Viva has the broadest reach of the three, particularly outside Yerevan.
That matters because Armenia is a mountainous country where a lot of what visitors come for, monasteries, gorges, Dilijan, Tatev, sits in terrain that does not suit mobile coverage. On the main roads and in the towns you will be fine. On the approach roads to some of the older monasteries you will not, on any network.
We name the network so you can check what we say against what other travellers report, rather than taking a marketing line on trust.