I wouldn't do it.
.AM is Armenia, a country bordering Azerbaijan, Turkey, Georgia. Unless you have a business in the Caucasus I don't see the use. FM is much more known than AM in terms of radio broadcasting, so I don't think .AM can have the same success as .FM
Armenia also has a decent economy of itself, and I doubt if they fancy the thought that foreigners use their ccTLD for different purposes, whereas .FM can use some foreign incomes as they have few people and companies themselves to buy domains.