Excellent idea, Toni. The 900 mHz headphones should do very well for you and
are quite legal. As it happens, they do fall in the 33cm ham band so if you're
working with high frequency ham gear you may be able to pick them signal up from
further away.
Tom
Tom Brennan KD5VIJ, CCC-A/SLP
web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html