Not really a work question but how do i deal with a friend who only calls me just to rant/complain?

Answer say your busy

Step-by-step explanation:

or just let it go to voicemail

Don't brush them off right off the bat. If they have time to rant about only their problems then you should be able to voice your complaints too. I'm not saying to turn the conversation into an argument but try to find a common ground and come to an agreement. Maybe they feel safe leaving their thoughts with you are just like rambling. Well whatever the reason you should also get the same respect you give of listening to your friends problems. All friendships are different but I hope I helped in the slightest.