I've done two business in an envelope before and it works great. But it's natural in that one business introduces the other business. I suppose one business could introduce two or more businesses but it may be too clunky to make it work.
Obviously there is the postcard route which has it's own set of advantages and disadvantages.
any ideas or insights?
Obviously there is ValPak which has 30+ businesses in an envelope although not in the form of a letter.