Cellphone

Most of the characters on Shadow Unit have cellphones. We know that some of the ACTF agents have customized ringtones or speed dial numbers for particular individuals.

Ringtones
Daniel Brady's phone rings three short, three long, three short (Morse code for "SOS") when Madeline Frost calls. 

Nicolette Lau's phone plays "Ride of the Valkyries" when Esther Falkner calls. She also has a "generic ring" for anyone not on the team. 

Chaz Villette's AOP "warbles" when Falkner calls. He also had a distinct ringtone for Natasha McAndrews. His laptop played the start of the Looney Tunes theme when Hafidha Gates called. 

Hafidha's ringtone for Stephen Reyes is Bugs Bunny saying "Ehhhh... what's up, Doc?" and for Solomon Todd is Johnny Depp saying "This is bat country!"

Faulkner's ringtone for Chaz is "Viva Las Vegas"

Speed Dial
Brady's speed dial for Reyes is "3". 

Hafidha's speed dial for Frost is "666". 

Lau's speed dial for Hafidha is "1". 

Other
Everybody on the WTF has Hafidha on speed dial, but we don't (yet) know all the numbers.

We also don't (yet) know any of the ringtones or speed dial numbers used by Daphne Worth or Reyes.

A "WTF?" message was sent to the team members at the beginning of episode 1x04, "A Handful of Dust". The question mark means that the case may or may not be anomalous. As Reyes told the rest of the team:
 * "And, for the record, if you get a question mark call in the middle of the night--" He turned his gaze to Falkner. "And you've got family--" He looked at Worth. "Or someone you think of as family--" He looked at Brady. "Or you're just having a good night, do not come in."

A message with a period or exclamation mark may mean the call is more serious.