I have a confession to make.  I am COMPLETELY unreasonable.
COMPLETELY.  Not one single drop of reason in this mind of mine.
Here's what I "don't understand".

1. 9PM is an unreasonable time to stop texting for the night.
2. You can't just stop texting.  Sometimes it takes an HOUR to wrap it up.
3. The conversations are important to his social life.
4. Obviously I don't want him to have ANY friends. 

I've seen these texting conversations.  You could sum them up in under and hour.
Here's an example...(as seen on his phone)
wat up
nun
brd
me 2
kewl
wat up
bzy
k
brb
k
wat up
brd, u?
brd
kewl
Seriously?  You can't wrap this up in under an hour?
I explained I trust him to stop at 9PM, but I am reviewing times.  If it continues to go much past then the phone and iPod will have to be in my possession overnight.
Pray for wisdom for me!!