This sounds like double taxation. The "subsidy" is something you pay for every month on your bill, which you also pay taxes on. So they get you for their imaginary cost of the phone, then they get the actual cost (minus what you paid upfront) as part of the taxes on your monthly bill.
I am all for paying my fair share of taxes, but when two groups in the same organization can't communicate and it costs me money, that upsets me.