There is no government postal system in Colombia. However, the private company 4-72 is Colombia’s de facto postal service, although it tends to be somewhat slow and unreliable. Residents rarely use the 4-72 service and usually turn to courier services such as Servientrega, which has many more branches than 4-72, although they are very expensive for sending mail abroad.
It is quite easy to get a SIM card and even an unlocked phone at Bogotá International Airport, although the price is of course higher. They are not hard to find in any other city either, just ask the staff at your hotel or hostel where you can go. Recharging is also easy and can be done on just about any street corner.
The providers you are most likely to see are Claro, Tigo and Movistar. Claro is the most expensive (a little), but offers the most coverage in the country if you plan to go off the beaten track.
Virgin Mobile might be the best option if you want cheap internet, as you can pay 20,000 COP$ for a month and get 350MB (plus 50 minutes, 10 sms and unlimited use of WhatsApp, a chat app almost universally used in Colombia) without needing a contract. It may take a little longer to find a place that sells sim cards. It should cost between 5,000 and 10,000 pesos.
From a landline phone :
To call from a fixed line to another local fixed line, dial the normal seven digits. To call from a landline to a mobile phone, dial twelve digits, always starting with 03, followed by the specified ten-digit number.
It is much more complicated to make long-distance calls within the country or abroad. Ask the person who owns the phone to dial it for you. If this is not possible, buy a mobile phone. Seriously.
From mobile phones and from abroad :
To call a Colombian landline from another country or from a mobile phone in Colombia, use the country code +57, then the eight-digit number (the first of which is the area code). To call a mobile phone, dial +57, then the ten-digit number. You can also enter “00” instead of “+”.
Internet cafes are easy to find in any city. Expect prices between COP$1,250 and COP$2,500 per hour, depending on the level of competition (e.g. cheap in Bogotá, expensive in the rest of the world). The quality of the connection is directly related to the centrality of the location and therefore inversely related to the price.