I hate to say it, but that is so sneaky I don't think I could trust him again if I was in your shoes. Changing contact names in his cell... what is he really hiding? How many messages were deleted that you didn't even see? What is really going on? It sounds like an affair to me. 

First of all, why do they need to communicate so much about SD22? My DH has not spoken to BM since my SD was 18, got married, and CS ended.

Second, to change her name in his contacts? Very sneaky, indeed. It's one thing to not mention the communication, it's another to outright lie about it when asked, and to change her name in his phone.

Some men lie about stupid stuff, just to avoid arguing, but this seems beyond that. Especially if you had an agreement to tell each other about communication with the exes. Has there been an excess of communication in the past? Overreaction (on your part) about said communication? It doesn't make it right but he could just be avoiding any backlash from you, or what he thinks will be backlash. My husband has been known to ASSUME how I will react to something and it never turns out good.

If something is going on with SD22 that he feels he must communicate with BM, why not just be honest about it?

One of two things:

he wants to maintain contact with her and is afraid you might think he still has a thing for her.

or

he still has a thing for her.

When someone is a lying ahole - well they are a lying ahole. You just never know what they are lying about or why. This guy isn’t a keeper. 

A few things come to mind...

Maybe BM sometimes makes comments about you that he thinks will upset you - just a nasty jab here or there or misplaced blame

Maybe he thinks what they're discussing about SD will upset you (like SD or BM want him to buy SD a car)

Maybe the contact is really nothing, but he doesn't have the nerve to tell BM to contact him less because he'll look whipped by you - he might not want BM knowing there's friction between you and him, especially if it has to do with her because she might leverage that to cause more friction between you

Maybe contact with your exes has been an ugly issue between you in the past but he thinks it's no big deal so he hides it - I'm thinking this might be your culprit because you said you came to an agreement about sharing ex contact. Did that agreement come out of fighting, mistrust or jealousy? He might want to avoid a fight with you over something he doesn't think is a big deal.

Don't jump to conclusions about why he's hiding this. If he has no issue with you talking to your ex, especially about kid stuff, he might really not get that it shakes you to your core -- men really do not understand women at all when it comes to nuances.

Don't tip your hand early that you know he's hiding it. Keep an eye on what the communications are about to see if there's anything bad going on. If there isn't, try to let it go. Even at 19, there are surely things that need to be said about SD. And he's with you, not BM. When you see it's really talk about nothing, try to have confidence that you're in and BM is out. As SD gets older, it will likely subside. Enjoy your relationship with him -- the best revenge is happiness!

First thing...stop asking why? Because there are too many veriables that can/will drive you crazy and exhaust you emotionally. Put on your big girl pants and just calmly and politly ask him about it. Parents of children will always have that parental relationship, and shared child. There will be things they need to discuss and not want to share with you. This happened to me as mine were growing up and after time I found out that SS got into huge trouble (quite embarrising to all of them) and the parents were working things out with him. A good step parent knows when to step up and when to step back.... and when not to step at all.  IF DH is a jerk, lying cheat... and you think these things would pursuade you to throw that relationship to the curb forever... then that will be a choice for you, and you alone to make.  Communication is key to a realationship - every relationship. And screaming, crying and yelling at is not communication. You need to have a serious kind hearted discussion with DH about this...the sooner the better. 

Just curious what the texts say? Since you saw a screenshot and know he changed her name in his phone and that they were texting about SD22, I'm assuming you saw some of them? What were they about?

My wife tried that sneaky sh@t when we first got together. She took her exes name off his contacts so when he called or texted it was just a number that showed up. She claimed it was because she didn't like seeing his name which was complete BS. They were joking around and getting along just fine so she obviously wasnt angry with him. I guess the guy she dated briefly before me dumped her because he went thorugh her phone and found some texts between her and her ex that made him end the realtionship with her. She said didn't like that he went through her phone and was possesive. There are two sides to every story. I think it was because she didn't want me seeing how friendly she was with him. I don't know why people lie when there lies are so obvious.

There is no reason for phone calls, unless like death in family!!  Everything should be text or e mail so there is a hard copy of discussion.  No Memory lane Bull S.  He should be walking down MEMORY lane with you. Not EX.  I can not understand how people alow this ?   If he needs personal space it with out EX 

It shouldnt be allowed. An ex is an ex for a reason. So what if they are the other parent to your kids. There job is to move forward with life and be a parent. That is all. And that is it.

If you do not then that is a red flag im itsself.

If you do then I say check other names in his phone for a second phone number.

One of the waus men hide other women is by inserting their names under good friends names in their phone.

Also...maybe bm got another phone and DH just loaded her in as a new contact. Happens...