Email or text...She may call if she is desperate, but we have not had any emergency and half the time, she wouldn't inform DH if there was....

We don't, but he didn't get any information about the kids when they did talk!

DH and BM communicate only through email/text. So far, no emergencies have occurred, but she has till tomorrow to notify DH of SD's out-of-state travel itinerary or she's in contempt of their new court order...we'll see if he gets an email or text in the 11th hour.

The neighbors call me. That's usually how we find out anything as her neighbor is my family (she somehow hasn't figured that out)
Otherwise he never knows anything, now there's a CO that should change or lots of contempt charges.

He doesn't get notified. Ever

SO doesn't get notified about anything, ever. GUBM didn't tell him that she withdrew SD from school. GUBM didn't tell him that they were moving until it was coming up on CS check time. GUBM doesn't tell SO anything about SD. So I have no faith that GUBM would tell SO if there was an emergency. The only thing SO does know is that GUBM does not take SD to the doctor or dentist ever - no vaccinations, no check ups, nothing - because SD is on SO's insurance (dental, vision, and health) and he gets EOBs in the mail anytime the insurance is used. So, his guess is that would be how he would find out about any emergency related to SD. Maybe.

Text or she might call if it is a true emergency....usually hours later than she should have, as well.

His mother if it really was an emergency.

She was allowed to call for true emergencies.

BM (per her boyfriend) refuses to contact DH abou anything skid related.

SD16 has been hospitalized several times in the last 4yrs and not one phone call. Once BM's sister called because SD cut herself and Aunt found her-BM's bf told DH if he showed up-he would be arrested since DH "has no claim to SD" (She is not DH's bio child but is treated as such) SD found out and had the bf removed from her room and BM caused a huge scene when DH DID show up.

She thinks he doesn't deserve to know squat when the kids are with her.

Sadly she lives in a town where a LOT of MY family lives including my Bff since kindergarten who lives 2 trailers down from BM and I hear a lot. Thankfully nothing bad has ever happened with SS11 but god help BM and her bf if anything did and they didn't contact DH.

Maternal and Paternal grandparents are the go-betweens. 

They only communicate via one of those coparenting apps. 

In the event of a true emergency they do have each other's numbers