simple ps2 controller question..

hi,
i jus would like to ask, if i use 2 or more ps2 wireless controller at a time,
will it hav any effect?
since the frequency used are the same.
what i know is every controller has their own ID, so there wont be any effect.
but so far, ive only seen ID from 0 to 9999.
after 9999 will the ID repeat itself starting back from 0?

tnx=)