What are some of the ways to keep in touch with old friends even after you leave college and busy in your jobs?

Whatsapp, Facebook, Twitter. Call them, text ...

Videogames. If this is one of your shared interests you can get on...

Like how other answers have already pointed out, you can use many of the social platforms to keep in touch with your old friends. I'd like to add a few suggestions after reading the updated question description. Don't simply reach out to your friends on these social networks. Furthermore, show that you care about their current life circumstances and listen to what they have been up to recently. For example, when you say how are you, don't just stop when they say "I'm good", try to show an interest in knowing what they have been doing with their lives. This would shorten the distance and bring new topics, other than reminiscing good old times (which would die out eventually), into your conversations with your old friends. Another way to keep your relationship with your old friends fresh would be to create new common memories together. My parents have been very close with their college friends for almost twenty years since they graduated, and one of the things I notice they have been doing is regularly take road trips to nearby cities. The trips don't have to be long, even 2-3 days and once or twice a year are enough. All of them have been up to different businesses or working in very distinct industries, but they are still maintaining the bond very well throughout the years because they have fresher shared experiences. Of course your choice is not only limited to taking road trips. On a side note, I personally don't think it's possible to keep "the fragrance of friendship fresh as before" and I would not even suggest you care so much about this. It is important to realize that your friends and you yourself, particularly, grow up and take different paths with your lives. Your friendships can be relatively well-maintained, but it'd be too high of a request for you to make on your friends to be just as close as you guys ever were.

Write to them Call Go to their home Social networks, texts and emails are too impersonal, if you want to create lasting relationships you should make an effort and hopefully they will reply in kind. If they don't, just use social networks. I've made friends in college, university and high school, all of which never made the same effort I made apart from a select few. They are the people you want in your life. It's not about the amount of friends you have but the ones that will always be there no matter what.

In the "old" times before email: write them a letter, if not so far away call (but intercontinental calls at that time would be prohibitively expensive). Nowadays email, maybe Skype, works in all places having decent internet connection.

I think this is a great question that my friends and I unknowingly solved while still in college.  During our senior year we set up a guys trip to Las Vegas during the 1st round of the NCAA basketball tourney.  It was just a short Thu to Sun trip with about 12 guys.  Everybody had a great time and committed to going to https://en.wikipedia.org/wiki/Las_Vegas for the tourney every year.  That sounds like one of those things you say to friends hoping it is true but really knowing it isn't. Flash forward 15 years later - the tourney is coming up in March and our Vegas trip is set with 8 out of the original 12 are coming.  There have been marriages, divorces, kids, cross country moves, job changes, IPOs, unemployment, and 2nd marriages and we keep going to Vegas mid March Thu to Sun.  Now I am obviously not saying you have to go to Vegas every year but one strategy to keep in touch is schedule a modest trip around the same time every year and start as close to college as you can (more on this later).  My recommendation is find something that suits your whole group and stick with it every year.  If you have to keep thinking of new events and different organizers somebody will inevitably disagree or forget to plan and the trip slowly crumbles. I believe this is a great way to keep in touch not only because you are guaranteed to see your friends at least once a year but you also have many email chains about the details, who can go, etc.  Back to when I mentioned start as close to college - the reason for this is to build tradition before there are too many competing priorities.  For example, my wife's birthday is middle of March and every 5 years or so conflicts with the trip.  But she understands that this is the 15th year of the trip (longer than we have known each other) and it is the only time each year I get to see a few of my friends - so it is established that we celebrate her birthday on the non Vegas trip weekend.  Having an arrangement similar to this for either family or work is much easier/more impressive when you say, "I can't miss this trip it is my 15th straight year."

2 years back, when there were just a few months for my classes to end, I wondered the same. Will we share the same bond after getting busy with the corporate life? Will it be possible to spend time with your friends in spite of the busy schedule? Will I ever be able to sit at ease and laugh at their silly jokes? I knew one thing for sure. The answer to these questions had to turn into a YES! Well my friend, remember one thing "No one is busy in this world it's all about priorities!" :) Plan for a kick-ass trek. A trek in the middle of the Western Ghats. Amid the nature. Your cellphones trying too hard to catch signals. Tired and exhausted, but still you have that little energy left to reach the top. You make it! You sit there breathing the fresh air around you. Recalling about the old times. No calls, no messages, no whatsapp. Just you, your friends and nature! Is there a better way to spend time with your friends? I don't think so! :) Here is how you make it happen. Choose a place and make an itinerary for 2 days. A rough plan - need not to be too specific. Drop a mail to your friends' group with the plan. Be clever to make use of attractive words in your mail (A little emotional blackmail is no harm, is it?) :D A detailed mail is better than "Hey guys, What's up? How about a trip?". Ping each of your friend and tell them to personally inform you if they decide on dropping out because a lot of times that one person is enough to cremate your entire plan. :P Let us assume, few of them drop out and few of them are interested but are too lazy to plan the trip. Save them the trouble. Do a little research. Break down the tasks - Divide and conquer! Let one of them decide about transport. Let the other decide on accommodation. You decide on a detailed itinerary. Now, your friends might need a little push now and then to get things done sooner. DO NOT MESSAGE! People see and forget :P  Call them. This way you are in constant touch with them till the end of the trip. Keep all your friends informed about the progress in the trip plans. Slowly you will see that people start responding. Remember the ones who said they won't be able to make it? Yeah, they are back in the game now :D Now you have everyone's attention! Go ahead and make bookings. As they say, first time is always the hardest. At the end of the first trip, I'm sure everyone will be looking forward to the next one. And in the next one, you will be speaking about all the funny things that happened in your previous trip and the chain continues. :D Well here is my secret, planning is more fun than the trip. I feel that is where you make that bond stronger. :) Celebrating birthdays. Plan for a small celebration on your friend's birthday. If you can't make it on the birthday, plan a weekend before or later because giving surprises on birthdays is just too mainstream :P Food Remember the birthday girl? Ask her for a treat. :D  Plan for a lunch/dinner. Discuss about the next trip :P Oh man! I am back with smileys in my answer. :\ Thanks :D It was a fun question to answer. :D