Can I use Viber without a SIM card? Viber is totally free, so that means that it doesn't require a SIM card. But if you don't have one, then you can only make calls while on WiFi.

Can I still use my Viber account even if I lost my SIM card that I use to register?

Simple answer, no you can't. The only ways to activate are via SMS or a call to receive the activation code and both methods require your phone number because the code will be sent to it. You are no longer in possession of the number you won't be able to activate Viber.

Will Viber work if I change SIM?

Change SIM card

If you put in a new SIM card, Viber will detect it. You can choose to change your phone number to the one attached to the SIM or keep the number you're already using on Viber.