Based on what you've told us, I completely agree with you.
I am curious though, you mentioned that you didn't put restrictions on at first. Once you realized he was doing something you weren't comfortable with, did you give him any warning/rules to follow before turning the phone completely off at certain times?
For example, once you realized he was sending texts in the middle of the night, did you tell him that sending texts between 10pm and 6am was not acceptable and then give him a chance to simply follow that rule?
I should have clarified that. When I said we didn't put time restrictions on it at first, I meant I didn't actually use the parental controls to turn the phone off at certain times. But he was given verbal rules with the phone regarding time restrictions when he got it. One rule was no phone or text after 10pm/11pm until he gets up the next day. That was non-negotiable. As well as handing it over at any time for us to check his texts, and if he was found using it in any inappropriate way (photos, during school time when it's not allowed, lewd texts, prank calls, etc) it was gone, no warning.
So no he didn't get any warning that I was then physically turning it off overnight. At that point he had already broken the rule. I had actually let it go the first time I checked the account & saw texts back & forth overnight, but then when he left it in my bathroom one night & it rang at 2:05am & there was a giggly girl on the other end asking for DS13, then I was done.
). If / when your son realizes it is up to him to do better, then I think you should turn it back on in the evening. And if he does really well, then I can see turning it on overnight. Let him demonstrate that he can be responsible. But let him know, if grades slip, it gets turned off again.
I agree. Lots of good advice on here from everyone - thanks!
DH & I often butt heads with rules & discipline. He grew up in a house with no rules or boundaries - kinda the hippe lifestyle, do what you want, when you want & screw responsibility. Life is about having fun & nothing else. I grew up in the complete opposite household - very religious, very strict, follow the rules or pay the price. So where he says I'm controlling, I see it more as parenting & guiding. I probably do need to loosen up a bit on some things, but I'm a firm believer in rules & following them.
I told him that is entirely too many and we were shutting the phone off at 10. He was staying up all night texting his g/f instead of studying or sleeping. He is doing better now and only had 7400 last month.
But alot of his texts are one letter as in K. 
What kind of rules (if any) are in your house for cell phone usage? Is it on 24/7 & they have full access to it at all times? I'm just curious because DS13 just thinks it's the worst thing ever that I turn his cell off at bedtime until he gets up (it's through Kajeet so it's 100% parent controlled).
I had not put any time restrictions on it when he first got it, then noticed he had been sending & receiving texts overnight (which really isn't all that bad I guess, but in my opinion, between school & sports he really needs to get a good night's sleep, uninterrupted.) So I turned off the cell from 10pm-6am on school nights, and from 11pm-9am on weekends (unless he was outside of the house at those times, then it stayed on). Recently his grades have been dropping slightly, mostly because of missed homework assignments. He had been doing his homework before bed, and from our observation, all he was doing between 8-10pm was texting or watching TV. So as his punishment for the detention he got for missing a few homework assignments (and his grades dropping because of it), we took the TV out of his room, and I said his cell is now off at 9:30pm on school nights. I said he can use the time now to be sure his homework is done, or to study, or to sleep if he has none.
DS13 says this is just absurd, none of his friends have a cell phone that ever gets turned off & they have full access to it 24/7. DH also thinks I'm "controlling" him too much by putting limits on the cell phone. So I said I'd poll all the great moms on the DIS & see if I really AM the only mom on the face of the earth that has rules about a 13-yr old & his cell phone.
I say I gave him a chance to manage the cell phone usage wisely, and he hasn't shown me that he can be responsible with it, so therefore as his parent (and the person that pays for his plan) I have every right to say when he uses it. DH disagrees & says even though we pay for it, we gave it to him & it's his, I shouldn't put restrictions on it.
So what rules (or not) do you have for something like this?
My daughter's are 15 & 16. Their cell phones are off at bedtime, off during dinner, off during school hours & off while driving.

DD14 (is in 9th grade) has unlimited texts but, her minutes are part of our family plan. She has never gone over on minutes and is well aware that if she goes over in minutes that she will be the one paying the bill. That is really her only phone rule. If she chooses to spend the night secretly texting instead of sleeping and wakes up exhausted for school, oh well guess she will be tired in school and at basketball or softball practice but, the grades better not slip or the phone becomes my property,(bedtime is 11pm on school nights, which means phone, TV and computer should no longer be in use and lights out). The texting at night thing on a school night I don't really consider a "rule" because I gave her my advice regarding the late night phone situation, meaning she should be sleeping after 11pm on a school night not staying up all night texting. However, if she chooses to ignore my advice on that issue then she has to live with the consequence of being exhausted all day, she has responsibilities (school, sports, homework, chores) and I still expect her to hold up her end.
*She has done the texting till 1 or 2 am thing on a school night a couple of times but, learned real fast that it just isn't worth it, she made the decision on her own to turn her phone off at night.
Well I think I'm worse than all of you!
DD18 1/2, HS senior and DS15, HS freshman, just now, a month ago got texting priviledges. I've always blocked texting during the school year and only allowed it during the summer. Too much access all hours a day to too many people just led to way too much drama that we felt was unnecessary. DD always said she was the ONLY kid she knew who didn't have texting. She was very, very unhappy about it.
But we have finally given and just last month let them both have unlimited texting and they seem to think they've won the lottery. They're so happy!
The only rule in place now:No texting/talking during school! Ever! (and of course for DD who drives, no texting/talking while driving either)
As far as late nights and such, we've never had an issue so we haven't addressed it.