Why a call to the customer solves most of the problems?
How often it has happened that your subordinate has exchanged furious mails with customer up to the point of confrontation, that you had to step in?
A project situation escalates due to a difference in opinion, quality of things delivered and many other things. Emails start cordially at first but soon turn nasty. Things escalate and leave project team members morale in tatters.
One of the reason such a thing happens is due to the fact that people cannot perceive what other side is thinking unless they are face to face or atleast on the face. A harmless comment or criticism may lead to contention. All the niceties then fly out of the window.
If you were a manager in middle of such a confrontation between your subordinate who is defiant and customer who wants to get things done his or her own way, what would you do.
The best way then is to make the employee pick up the phone and call the customer ( or better if possible , visit customer's premises). People are generally nice when they see each other. After all no one likes to be called rude and offensive . The chances of resolution then gets higher. When people can’t see each other they become less polite and disrespectful often under when they are in stress.
Look at the trolls on internet. They are rudest and hide behind anonymity.
So here are the things as a manager you can do in the order of priority or teach your team members about
Visit the customer
Video-Con with them
Talk on the phone
As a manager you best bet is to push employees to pick up the phone and call the customer. That would save you a lot of embarrassment later on.