<human>: Can you summarize the given text in a few sentences?

My friend (currently pregnant with Baby #5) has been having some serious marital issues.  In the last 5 months, her husband has moved out, they've had screaming fights where things were thrown/broken, and as an outsider, he seems incredibly manipulative.  He will do just about anything to stay married, convince her that he should be allowed to treat to her like shit (because she is a "crappy wife"), and then be free to do anything and everything he pleases with no responsibility to his family.

This weekend, Friend went through her husband's phone and instantly regretted snooping.  There was reference to "smashing that tight p#$$y", recording it without her knowledge and something about the girl's boyfriend not "being up on his d!@k game."  It's pretty obvious that he has either cheated or plans to cheat with the girl referenced.  She copied down the number and called it.  When a woman's voice answered, she hung up.  Friend is now wanting to call back and speak to this person, mostly for the purpose of letting them know that he is married, etc.

If you were in her position, what would you do?  Call and expose Husband?  Call and find out who she is?  Do nothing?
<bot>: Friend wants to blow up her husband's cheating potential with the truth and wants my help.  Worst idea ever or advice on how to do this properly?