No it won't, I have been using mine almost two years now and I have never had a problem and I have never read of anyone else ever having problems. Ask your brother how it will damage the radio? It's no different then using your radio at the field.
Just make sure you take the crystal/module out of your radio so it doesn't send out any signal. Some people say if you leave the crystal/module in and the antenna down when using the radio with a sim it will get hot. If you leave the crystal/module in the radio, just pull your antenna out about a foot, that way it won't get hot (but it's best to just take it out).
I take my module out of my radio when using on the sim, it will make the battery last a lot longer (it's not sending any signal).