Just want to throw my thoughts in too--it did get better for me too about 1-2 years after divorce. My kids were older (11and 13), so I got them their own phones and he was directed to communicate directly with them. They've each gone through phases of ignoring his calls and texts or being "busy", and I initially got bombarded with accusations--but ignored them and told him he could always come talk to the boys if he had an issue with their communication. He never did.
It was a crazy, stressful time, and I feel for you!
I was actually pretty proud of my boys in that, after being a jerk, then a baby, then a jerk...they held their boundaries, and 3 years later they seem to have reasonable communication on their terms.
If you don't engage in the crazy, they do sometimes get bored and go find other crazy. The downside is that they'll almost always come back to their kids if they get bored. (No, not to be a great dad or anything like that--to get a "fix".)
Our children will be amazingly strong people!