Restart it. Or go into Settings>Applications and force close some stuff you don't need.

 

Mine never slowed down, but I got to know the phone for a week and then did a factory reset on it. Might be somthing you want to do.

 

I would definitely not recommend something like that for a simple problem like this.

 

Any particular reason why?

 

You want him to do a factory reset just because he's got a problem with his phone that can be fixed by either a power cycle or a simple hard restart?

 

Yeah, different scnerio/situation, I see your point.

 

I'm sorry if I sounded harsh but, to me, a factory reset is probably the most drastic measure you could take.