For a very long time, the state-owned Bulgarian Telecommunications Company (BTC) had a monopoly on fixed telephone networks.
Larger areas, such as Sofia, Plovdiv, Varna, and Burgas, are subdivided into zones.
], the intensive process of replacing the old analog switches with modern digital ones completed.
With the increase of subscribers (and an international requirement), all (except Vivacom, which started operations in 2006) acquired new access codes.
When these limits were also to be overwhelmed, seven-digit subscriber numbers and single access codes per operator were introduced, hence M-tel (now A1) reverted to 088 (+7 digits) only, while Globul (now Yettel) took the old M-tel code 089 (+7 digits), and the rest were freed up.
This change provokes an error in citing mobile numbers, quite similar to that of erroneous UK telephone codes.
However, unlike the situation in UK, this error has no effect since a mobile number must always be dialled with the access code.