If a project is a team project then you most certainly can (and should).
It is recommended that you create a group on Viber and add all the members to the group. Alternatively, you could use Facebook groups but you should take into account that Facebook groups are not private and the Facebook mobile application is unstable and cpu intensive. As a result of this, members of your team that have old devices could encounter problems.
If the project is a individual project then although you could talk to each other and exchange ideas, actual cooperation is not feasible since each resulting project should be different.