There a number of ways for crew members to contact each other. Here are some of those ways
Many users of ezccs share their contact (under Passwords/Options). Where you see a yellow highlighted uID you can touch that for Contact information. Additionally if there is a crew image that you have popped up, press and hold. If you use the View All Crew Link (Just Crew in EBB) you can tap a crew member image.
Below are some examples:
Many FA's share their phone numbers in Master Schedule. You need to know the uID. Use the Master Schedule function in ezccs and the phone number, it available with be selectable.
This symbol is what United supplies as a crew communication system.
Tap on the red Crew and then tap on a crew to see a contact option.
Pilots my also use the Crew Companion system to contact crew members.