Monaco is a sovereign micro- and city state and a principality located on the French Riviera. France borders the state comprising 2 km2 on three sides. That’s why there is no need to buy a special SIM card for Monaco as French antennas mostly cover it too.
In Monaco 2G is on 900 and 1800 MHz, 3G on 2100 MHz and 4G/LTE started in 2013 on 800 and 2600 MHz (bands 7 and 20).
EU Roaming EditSome providers from the EU voluntarily apply EU roaming regulations in Monaco. When roaming with an EU-issued SIM card, check with your provider first, or prevent your phone from roaming on Monaco Télécom by making a manual network selection and stick to French networks instead.
Monaco Télécom Edit
Monaco Télécom is the main telecommunication and only mobile network provider with own antennas in the Principality of Monaco. The company was founded in 1997 following a decision by the government of Monaco to privatize the state-owned Office Monégasque des Téléphones.
For prepaid, it has a monopoly and charges amongst the highest rates in Europe. The starter set alone of their prepaid card will set you back €19.90 and gives only 100 KB of data. Reasonable data packages are absent.
Monaco Télécom has a roaming agreement with Orange in France and users of these networks can use each other’s networks without surcharges. So for now, it’s better to buy a French SIM card to be used in Monaco than a local one.
Like in France, having a French bank card and French bank account it's a totally different story. Then you can take advantage of competively priced forfaits (= contracts), which are available without a minimum term too, and are valid in all of France on Orange and in Monaco.
French providers in Monaco Edit
French providers cover Monaco too. If you have a choice, Orange has the best coverage through its roaming agreement with Monaco Télécom. But SFR and Bouygues Télécom are other options too, because their antennas reach the principality too.
In April 2016 the governments of France and Monaco signed a spectrum coordination agreement that allows French mobile operators to deploy their own base stations in Monaco. French mobile customers have experienced patchy service when trying to connect to their networks when in the principality. French mobile operators haved signed agreements with Monaco and added new antennas in Monte Carlo covering all of the area in 4G/LTE.
It has been a different story with Free mobile, however. Free usually has a roaming agreement with Orange for areas where it doesn't have own coverage in France. But the roaming contract between Monaco Télécom and Orange overrode their French agreement. This led to an effective black-out of Free in Monaco (source in French). Even as the majority of Monaco Télécom was taken over by Iliad in 2015, which happens to be the parent company of Free in France, the situation only slowly improved. In 2017 Free users report now better data rates in the city too with a stable 3G coverage in most places, albeit still no 4G/LTE yet (source in French). In 2017 Free mobile signed an agreement with Monaco Telecom to rent spectrum for 4G. So this is likely to improve soon too.