2. Battery dead/no credit/no signal
4. At work/school
5. Watching a movie
6. He's with another girl
Ok, this is the worst possible reason - and let's hope it's not the case with your boyfriend!
If it's any reassurance, most guys would usually put together a quick and shifty looking text to cover their tracks rather than saying nothing at all.
7. He fell asleep
Hey, it happens to all of us...
8. He's drunk/at a party
Not an excuse you should accept, especially if his attention is straying towards drunk girls instead!
9. He's nervously trying to think up something cool, clever, funny ot romantic to text back - but he can't think of anything...
This is a very likely reason. Some guys over think texts, especially if they know how important hearing from them is to you.