Contact selection

Can you select contact and then send message to them at once

Yes. This is how playsms works.
Go to Myaccount -> Compose message.
Type your phone number and then your message.

ps: You need to have a valid gateway working

I mean first you select multiple contacts like check button and then send the message

@vmos already said how to. If you find another way you should try to use “Phonebook” (My account --> Phonebook) or download contacts from file and bulk.

By Contact selection i meant that onw must be able to select from phonebook through check boxes?
is that possible

The phone book works like what you need, search then select and it will be added to the send list.