We chose not to include birthdays in our parenting plan, which just says 'alternate as determined' . Because our kids are older teens we knew they would have their own ideas about how they spent their special day, so we will leave it up to them when/where they celebrate. Our oldest is turning 18 this year anyway, and for these next few years the youngest's birthday happens to fall on or next to 'dad' weekends, so even if she chose not to see him on the day of she'd see him within a day anyway.
I chose to not include parent birthdays in the plan either. My birthday is right after Christmas and I worried insisting on having the kids with me on that specific day would just complicate whatever holiday/vacation plans we tried to set up. We do have an off-the-books agreement that we can have the kids on our own birthdays if nobody otherwise has plans.
As far as communication the day of, we have in our agreement that everyone has unrestricted phone/email/etc access anyway. We don't have any sort of schedule specified because the kids are old enough to manage on their own.
In real life, after having this un-plan in place for a year, it is mostly working for us. My ex has been rather "loose" with his parenting time anyway, so I think he enjoys being able to come and go as he pleases.
Our visitation calendar has only been in place since Nov 1, but we've gone through a full birthday cycle:
Child #1 b-day: Original plan was to split weekend 50/50 with dad, but dad ended up "having a friend stay over". Dad came to our house the day of for cake for 2hrs.
My b-day: Just happened to fall on a 'mom' weekend anyway.
Child #2 b-day: Birthday fell midweek; MIL was in town so Dad took them all out for the day, then we all met back at my house for dinner/cake.
Dad b-day: Happened to fall on a 'mom' weekend, so I reminded him three weeks before he could have the kids if he wanted. He gave me three days' notice he was actually going to take them, but ended up cancelling the day before to take his girlfriend out of town. Pissed off that he canceled again, the kids refused to phone/email him; I ended up in the doghouse.