Yes. You can start chatting with your phonebook contacts on Teamchat. If they are registered on Teamchat, they get added to the group instantly. And if they are not, they show up in the 'Pending' section in group info. Teamchat automatically sends all the 'Pending' email IDs an invitation to access the group by registering on Teamchat, whereas the 'Pending' phone numbers can be invited by you through text.
Please note: Your contact added by phone number will only see your chat if he has added and verified his number on Teamchat