It is not possible to install and use viber on more than one phone with a same mobile number. When you install and activate viber, only the newest activation will remain valid. All the previous installations will be void and when you try to access old installation of viber on a different phone, you will be asked to activate viber.
The mobile number is used only at the time of activation. Once activated, Viber will continue to work even if the sim card is removed or a different sim is used. So you are free to use any sim/number once activation is complete. But if the same mobile number is used to activate viber on another device, viber on first device will be de activated.
Exception is Viber for PC. You can install, activate and use Viber on PC with the same number that you use on your phone/tablet. The activation code for Viber PC will be sent to Viber on your phone and this needs to be used to activate viber on pc. In this case, Viber on phone will continue to work and it is possible even to switch on going calls between your phone and pc.
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