Johannesburg is the telecommunications hub of South Africa, which ranks 23rd in telecommunications development in the world. South Africa's telephone system is the best developed and most modern in Africa.

Johannesburg hosts the headquarters of numerous local and international operations, and serves as the base for multi-nationals operating in the rest of the continent. South Africa has approximately 4.92-million installed telephones and 4.3-million installed exchange lines. This represents 39% of the total lines installed in Africa. Some 58% of Johannesburg's households had a fixed line telephone in the home in 2001, an 11% increase over five years. In 2003 the industry was reportedly worth about R81-billion. And 85 percent of the sector's activities occur in Gauteng.

South Africa's sprawling geography has required it to invest in a large transmission infrastructure that covers about 156-million circuit-kilometres. The transmission network is almost wholly digital. Digital microwave and optical fibre serve as the main transmission media for the inter-primary network, interconnecting all major centers, including Johannesburg. The two licesnsed land line companies are Telekom and Neotel. 

South Africa has switched to a closed numbering system. As of 16 January 2007 has been mandatory to dial the full 10 digit telephone number including the three-digit area code even for local calls. The trunk prefix is still '0', with the system generally organised geographically. All telephone numbers are 10 digits long (including the 3 for area code), except for certain Telkom special services. When dialed from another country, the '0' is omitted and replaced with the appropriate international access code.  The country code is 27. The telephone area code for Pretoria is 012 and for Johannesburg 011. If you are calling from outside South Africa, replace these codes with +27-12 and +27-11 respectively.Numbers were initially allocated when South Africa had four provinces, meaning that ranges are now split across the current nine provinces.

00: effective from 16 October 2006 and mandatory from 16 January 2007.
01: The old Transvaal International access code province, currently comprising Gauteng, Mpumalanga, Limpopo and part of the North West:
010: New overlay plan announced for Johannesburg (proposed November 2001-not in use)
011: Witwatersrand region around Johannesburg, currently code for entire Greater Johannesburg
08: Special services
080: Toll-free
081: Currently unused (?), was car phones
082: Cellular: Vodacom
083: Cellular: MTN
084: Cellular: Cell C
085: Cellular: Reserved for a 4th operator and for USAL license holders
086: "Sharecall" and premium-rate services
0866: Premium-rated Fax to email service
087: Value-added services (VoIP among others)
088: Pagers and Telkom voicemail
089: Maxinet, for polls and radio call-in services