Tanzania has charged two chief executives of telecommunication firms with economic sabotage.
The managing director of Viettel Tanzania, trading as Halotel, Mr Le Van Dai and managing director of Zanzibar Telecom, trading as Zantel, Mr Sherif El-Barary were arraigned along with four others on Wednesday.
Mr Dai is a Vietnamese national while Mr Barary is Egyptian.
The other four suspects are two Chinese citizens - Lei Cao and Huang Yu Meng of Shunshe Company Limited, and two Tanzanians - Jimmy Mosha and Willy Ndoni working for Halotel as business supervisor and marketing manager respectively.
They are accused of conspiracy, fraud and tax evasion and are said to have caused the government losses of more than Tsh1.2 billion (about $530,000) in levies.
The offences include use of unregistered SIM cards, operating without licences, illegally importing and installing communications equipment, and fraudulent use of telecommunication networks.
According to the prosecutor Jacqueline Nyantori, the offences were committed between January 2017 and April 2018.
Ms Nyantori told the court that the accused conspired to evade rates payable for international messages by terminating them using unlicensed gateways.
The court was told that last year, Mr Cao and Mr Meng imported into the country 44 voice over internet protocol (VOIP) gateways with no serial numbers and without permits from the Tanzania Communication Regulatory Authority (TCRA).
The prosecution said the two men installed and maintained the equipment at Spring City Building in Kinondoni northwest of Dar es Salaam central business district.
The equipment allowed them to illegally by-pass TCRA telecommunications traffic monitoring system.
The accused were also found with 281,272 unregistered Halotel SIM cards and 11,920 Zantel SIM cards.
The suspects did not enter plea because the charges, which fall under the Economic and Organised Crime Control Act, can only be tried by the high court. The judge at the Kisutu Resident Magistrate's Court, where they appeared, remanded them in custody pending trial.
Halotel is owned by Vietnam-based telecoms operator Viettel and Zantel is part of Sweden's Millicom.
Other mobile phone operators in Tanzania include Vodacom, a unit of South Africa's Vodacom; Bharti Airtel; Tigo, part of Sweden's Millicom; and state-owned Tanzania Telecommunications Corporation Limited (TTCL).