HELP!! ENGAGEMENT PARTY!!

My fiance and i just got engaged and only our parents and siblings know. Our parents are very busy and dont have time to plan a party for us so we decided to throw an engagment party for all our friends so we could tell them all at once. Our parents plan later to throw a joint "family" only engagement party. My question is should i send invitations out to all our friends or just call or what? Also if i should send out invites what should they say? thanks in advance :)