How to register Zalo when not using the phone number Vietnam?

Specifically, we're at in Thailand, they are using a telephone number of the Thai network, I want to use Zalo how they must not use the phone number of Vietnam, one knows not only help themselves with . Because the calls from abroad to Vietnam are very expensive, so I want to use Zalo to chat with relatives because this is your favorite applications and a lot of Vietnamese people to use while his family and all lovers anymore.