The Fallout has no classes though.
Back to the topic. The idea is neat, but it would demote the current requirement for high demo skills for exact timing. However it is a fun idea and may be quite "balanced" (this word is a main killer of many cool suggestions) if the demo skill required to craft such explosive would be high enough.
But I see lots of people changing channels and typing "asdf" to occasionally explode someone's channel. Also it would be fun to trade such explosive to some random player with "1337" channel set and tell him: "Let's meet in NCR, send me "I'm here" on 1337 freq. when you're there".
Or play russian roulette. One player sets a frequency and puts the bomb down, other players pass it and start to say something on random channels.