According to the government, 60% of the 1400 people currently held in immigration detention centres in Australia have a criminal history (which could include unpaid parking fines). So, 40% of immigration detainees have no criminal history at all.
The government is keen that these people not have access to mobile phones. It has been trying to achieve that since 2017, when it first introduced proposed amendments to the Migration Act accordingly but failed to get them through the Senate.
In 2018, they tried a different tack, imposing an
administrative ban on mobile phones in detention centres, however that was declared
illegal by the Federal Court.