There are two possibilities for this scenario.
The first is that this free broadband requires a pre-payment. For example, deposit 100 yuan, and then the 100 yuan is returned 12 months, so that you can give a free broadband.
The second is that the 100 yuan is the installation fee and material fee, after the user pays 100 yuan, Unicom returns the 100 yuan through the way of reduction
Install Unicom broadband need to recharge 100 yuan. It may be due to the fact that when you open broadband, the Unicom company is engaged in activities, you can charge 100 yuan to give concessions, mobile phone packages are not free for broadband, and broadband is also charged in mobile phone packages.