I phoned their support line.
Good news, phone line subscription is not required. Buy a package and use it. Prepaid tarif apply after bundle run out (20c/MB - not bad).
Bad news, I am in the coverage for phone line, but not for high-speed data.
Bad news, modem from the deal do not support external antenna connector, so I cannot extend coverage. Router has, but in the price range R1400.