I've never used a comms pack with a vibrate function, but I'm wondering if the motor I suggested will have enough of an effect to be noticeable. It's really designed for something worn in the pocket, or as mechanical feedback for a handheld device. Worn on a belt clip I'm not sure if there will be enough coupling to the body for it to be noticed. I'll have a play with the ones I've got spare and see maybe strap them to one of my walkie talkies - should have a similar sort of mass. I think they'd have to be mounted on the chassis rather than the pcb anyway. This is the one I bought; http://www.technobotsonline.com/10mm-vibration-motor.html And if you go to the downloadable datasheet you'll see it wants an 85mA startup current, and runs at 75mA normally, at somewhere around 3V. I was sort of thinking that if it's something people wanted, they could bodge it themselves, maybe just with a power supply and a transistor off of the LED. Maybe a solder pad somewhere around the lamp circuit that would allow people to sniff off the call lamp signal? Have you thought about a source of the belt clips themselves? Maybe something that you could include in the panel drawings and group buy? Just some folded sheet would do the job. I find that the off-the-shelf ones for hobby projects don't stay on all that securely - the clip isn't long enough to properly grab around your belt. I've got a stash of ones rescued from Kenwood UHF handhelds, but it's not enough to be able to offer them to others I'm afraid! These ones are sprung but I don't think it's something a custom made one could be all that easily.