Question: When was the Finnish telecommunications company founded which wholly owned Starman Estonia since December 2016?

Context paragraphs:
AS Starman: Starman is an Estonian cable television and Internet service provider company founded in 1992 and located in Tallinn.  Since December 2016, Starman Estonia is wholly owned by Elisa.

Tanzania Telecommunications Company Limited: Tanzania Telecommunications Company Limited (TTCL) is the oldest and largest fixed line telecommunications company in Tanzania.  The company comes forth from the former Tanzania Posts and Telecommunications Corporation in 1993.  TTCL was wholly owned by the Government of Tanzania until the partial privatisation of the company on 23 February 2001.

Kaj-Erik Relander: Kaj-Erik Relander is a Finnish businessman.  From 2006 to 2010, he worked for the venture capital firm Accel Partners in London.  Previously he worked for seven years at the Finnish telecommunications company Sonera, where he was CEO for six months in 2001 before resigning for personal reasons.  In 2002, Sonera merged with the Swedish telecommunications company Telia.

Optus: Singtel Optus Pty Limited is the second largest telecommunications company in Australia.  It is a wholly owned subsidiary of SingTel (a company headquartered in Singapore) since 2001.  The company primarily trades under the Optus brand, while maintaining several wholly owned subsidiary brands, such as Virgin Mobile Australia in the mobile telephony market, Uecomm in the network services market and Alphawest in the ICT services sector.

Sony Mobile: Sony Mobile Communications Inc. is a multinational telecommunications company founded on October 1, 2001 as a joint venture between Sony and Ericsson, headquartered in Tokyo, Japan and wholly owned by Sony.  It was originally incorporated as Sony Ericsson, until Sony acquired Ericsson's share in the venture on February 16, 2012.

Portugal Telecom: PT Portugal SGPS SA (also known as Portugal Telecom or PT) is the largest telecommunications service provider in Portugal.  Since June 2, 2015, PT Portugal is a wholly owned subsidiary of Altice Group, a multinational cable and telecommunications company with a presence in France, Israel, Belgium & Luxembourg, Portugal, French West Indies/Indian Ocean Area and Dominican Republic (“Overseas Territories”) and Switzerland.  Its assets in Portugal were sold to Altice in 2015 in a move of its owner, Oi SA, to reduce debt.  The African assets were mostly sold for the same reason.  Portugal Telecom, SGPS SA was split in separate companies: PT Portugal (owned by Altice) and Pharol (formerly PT SGPS), which owns a 27,5% stake in Oi.

Mahanagar Telephone Mauritius Limited: Mahanagar Telephone Mauritius Limited (MTML) is a telecommunications and Internet service provider in Mauritius.  MTML was founded in 2003 as a wholly owned subsidiary of Mahanagar Telephone Nigam Limited (MTNL), an Indian Government-owned telecommunications company.

Zain Group: Zain Group (Arabic: مجموعة زين‎ ‎ ) is a mobile telecommunications company founded in 1983 in Kuwait as MTC (Mobile Telecommunications Company), and later rebranded as Zain in 2007.  Zain has a commercial presence in eight countries across the Middle East with 45.2 million active customers as at 30 June, 2017.  The Vice Chairman and Group CEO is Bader Nasser Al–Kharafi, who was appointed in March 2017.  Approximately 24.24% of the company is owned by Kuwait Investment Authority; 16.26% is owned by Al-Khair National for Stocks & Real Estate Co; only shareholders that own above 5% are disclosed.

Elisa (company): Elisa Oyj is a Finnish telecommunications company founded in 1882.  It was called HPY HTF until July 2000.  The mobile operations of Elisa were previously known as Radiolinja.

PlusTV: PlusTV was a Finnish digital terrestrial television distributor owned by Finnish telecommunications company DNA.  It is one of two pay television distributors in the Finnish terrestrial network, the other being Canal Digital.

Supporting paragraphs: AS Starman Elisa (company)
Answer: 1882