Can anyone tell me what would be the easiest and cheapest way to access the internet? How common are HotSpots (biggest cities or towns) ? Can I rely on it or would be easier to buy 'pay and go' SIM card ? I am not going to use it for any social network or anything like that (except of SE Travel :) ). Google maps, general googling and highly possible online banking (from time to time) would be mostly used.
In the big cities, there is a sufficient number of trendy cafes and restaurants, not just aimed at tourists, that offer free wifi. But, most 'regular' joints, targeting Colombians, won't have wifi.
So, if you only occasionally need to be online, you're probably good to go. If you need to be able to go online when you want to, you should look into a local sim.
I can now share my experience... There was no need to buy any local SIM cards as WiFi is almost everywhere: hotels, hostels, B&Bs, restaurants and buses (long distance ones). Just to remind you, be sure your mobile is fully charged and definitely have power bank handy (especially on the bus).
Just buy a colombian prepaid simcard. Major carriers (Claro, Movistar or Tigo). I have used Movistar and Tigo, and I could recommend movistar. It has LTE, and the coverage and signal strength are good.
Movistar offers 7 (US $4.50) and 30 days plans (US $ 13), so is the cheaper and most convenient option here.
In the major cities, Bogota, Medellin, Cartagena etc you will find lots of free hotspot places like restaurants, pubs and bars. Even if you don't see hotspot advertised then feel free to ask the waiter for the logon details. Unlike in other countries most hotspots don't require any online registration, simply select the network and add the password for immediate unlimited access. If you are planning to travel about or want internet access in the street then a prepaid sim is your best bet, these are not locked so should be available to use on any cell phone. Again rural areas might suffer from weak mobile signal and hence poor internet but in most towns and cities you will get good coverage. I would recommend Claro and Movistar as the best providers.