In Russia, even domestic operators charge different rates depending on whether users are inside or outside their “region of origin.” A number of legislative attempts to eliminate internal roaming have failed due to opposition from operators.  After the annexation of Crimea in 2014, Russian operators were criticized for not directly offering their services inside Crimea, although they were formally recognized as a regular federal issue within Russia.  This type of roaming involves the possibility of joining the network of a foreign service provider. It is therefore of particular interest to tourists and international business travellers. Overall, international roaming is the simplest [ever?] with the GSM standard, as it is used by more than 80% of mobile operators worldwide. But even in this case, there may be problems, because countries have assigned different frequency bands for gsm communications (there are two groups of countries: most GSM countries use 900/1800 MHz, but the United States and some other countries in America have assigned 850/1900 MHz): for a phone to work in a country with another frequency allocation, it must support one or both frequencies of that country and therefore be sort or quad. If international roaming allows the traveller to stay in touch during the trip, it can also result in considerable costs for users. Indeed, the use of mobile networks outside the country of origin can result in a large billing by the original mobile data operator.  In order for a participant to register on a visited network, a roaming agreement must be reached between the network visited and the domestic network. This agreement is based on a series of testing procedures called IREG (International Roaming Expert Group) and TADIG (Transferred Account Data Interchange Group).
While IREG tests are supposed to test the proper functioning of established communication connections, the TADIG test is to verify the feasibility of the calls. This type refers to homelessness between two standards. This term is now widely used in mobile communications, where CDMA customers, in particular, wish to use their phones in areas where there is no CDMA network or where there is no roaming agreement to support roaming to the standard used. In Europe, there are hardly any CDMA networks. Most OF CDMA`s clients come from America or the Far East. In order for them to roam in Europe, inter-standard roaming is the solution. CDMA customers arriving in Europe can register on available GSM networks. On 11 June 2013, the European Commission voted for the first time to abolish roaming charges for mobile phones.  Most mobile operators advise against it or prohibit permanent roaming, as they must pay per minute rates to the network operator on which their customer travels by roaming.