My daughters are 17 and 13. The 17 y/o typically has over 1000 txt messages/month. The younger girl has less than 400 and half of them are to me. This is a new generation. They have this technology that we could never imagine. It makes them accessable 24/7, but too much of anything is never good.
Since your son already knows there are limits to using the phone, expand your limitations. Tell him there will be no messaging after bedtime, and have him send a mass text to all his friends. If he breaks this rule, take the phone and charger to your bedroom at night. Your son can get the phone back the next day, and read all the txts he missed.
Hold onto his phone while in Fla. He can let his friends know that he will be on vacation, and his "rents" are limiting his phone use. You can determine when he can have phone time. His friends and he will have to deal with it.
Set limits you are comfortable with and enforce them without emotion. Don't let him suck you into a power struggle. It's simply a rule.. and treat it matter of factly.
Lastly I try to remember that this is how they communicate. I don't want to punish my daughter or cut her off socially.. but there are limits to everything in life, and being available to your friends 24/7 is not healthy. There has to be "down-time" .. personal space where they can relax and get to know themselves.. Attention needs to be given to family, school, sports, activities, and other obligations of day to day life. I think it's an important lesson to set personal limits. And an important skill for any child to learn. For me this is an excellent way to show him how to do that.
In our school district, if a kid is caught with a cell phone while in school or after school activities, the phone is confiscated, and can only be reclaimed by the parent. Once my daughter was caught texting during a class, and she didn't get her phone back for a month. That was the end of that.
Good luck. It's never easy raising a teen.