Needless to say, having a cell phone is convenient. I didn't need to completely avoid using one to realize this; however, after one year of abstinence I can say that this convenience comes at a cost, one I'm still not ready to put up with.
Constant access to technology
First of all, cell phones provide technology at your fingertips at any moment, this might look like a good thing, but it actually isn't. In the last year I got rid of many annoying and rude behaviors and bad habits caused by this constant access to technology. Here are a few examples:
The web
Common situation: you are talking to your friends, and suddenly a question arises: when did this happen? Who did that? Where did he go? Most of the time nobody cares about the answer to this question, the discussion simply moves on; but there is always someone that has to look things up on the web and interrupt the natural course of the conversation to tell you when it happened, who actually did it, where he went.
Being able to look everything up on the spot also takes away the need to figure things out on your own, which is an important skill, if you ask me. e.g. there is no need to look up where the nearest bar is: just walk around the city block and you'll find it. When travelling, I often tried to remember every turn needed to go from A to B and got lost, but this only happened the first time: now I know where to go, and I also know many interesting places close to B.
Don't look at the screen all day. I don't know what's so important about a cat playing the piano but I can guarantee you that the real everyday world is probably more important than that.
Music
Since I got rid of my phone I stopped listening to music when I'm traveling. This simple habit is everything but innocuous: walking around focused on something that isn't the world around you is both dangerous and a real waste. Just by giving your ears the chance to listen to what happens around you, you let your mind free to wander and notice every funny, weird or interesting aspect of the present moment. This might look a little naive, but it's really astonishing how many inputs the world gives us, we can't just waste them to listen to our favorite song with half an ear.
Careless organization
Being able to communicate at any moment remotely encourages careless organization. There is no need to be on time if you can just send a text message saying "I'm late", there is no need to agree on where to meet if you can just send me your location when you get there; when I go out with my friends this bites me every time. I only have access to the web when I'm at home, so I can never be updated about last-minute changes to the plan. On the other hand, when I need to organise I try to think about every possible variable beforehand, because I know I won't be able to adapt my plans on the fly.
Social connections
After one year without a phone I noticed that my friendships have radically changed. Nowadays most social interactions take place on the internet, using some chat service like Whatsapp, Telegram or some other social network. I don't use any of those: I use XMPP and e-mail. Trying to take my friends away from Whatsapp is already a hard task, but making them realise that it's just impossible for me to have real-time communications is hopeless. I don't have access to the internet when I'm travelling, I don't have my computer on all day, so if you are lucky I will reply within a couple of hours, if you aren't it will take me the whole day.
Most of my friendships survived the change, some didn't, but all of them changed: the most important interactions no longer take place on the internet nor mediated by technology. If I need to talk to someone my first option is always meeting them, this was not the case a couple of years ago.
Some of my friends still don't understand my choice, and think I just want to make their lives harder by not being in all of their Whatsapp groups, most of which are redundant and worthless when it comes to organization (see the previous point).
Conclusion
Last year changed me radically as a person: I learned a lot and changed the way I approach everyday life. Not every change is completely positive, I admit some of my friends still don't understand or approve my choice and this caused some friction.
What makes me sure about my choice is that my primary concern is not convenience, I think this is really important to understand. In these lines I've only addressed practical consequences of my choice because most of the critiques I get happen to be focused on this aspect, but this is not the only, nor the most important, parameter by which I judge this last year.