Since the 1970's, Intelligence is able to record/hear every word uttered within 10 metres of a working telephone.
Now, they can even tune in to cellphones that are switched off. (For all you negative nancy's, this is true , evidence of a switched-off recording has already been used)
Yeah they probably do notice the uttering of words like that, but they couldn't care less about some useless stoner babbling on about a terrorist attack they are planning.

Also, I don't think many terrorists talk like that;

"Ee Ibrahim?"
"Dirka dirka muhammad jihad?"
"We iz goingk to blow up the president withz a bomb"

That would be stupid.