When shopping for a new iPhone X today, you are considering buying it outright or on a $24$ month plan $($without data and sim plan$).$

Buying it outright costs $$999$ while on a $24$ month plan, the repayments are $$43/$month$.$ The opportunity cost of capital can be used as a discount rate and by purchasing the phone, you give up investing in shares which earn you $6\%$ p$.$a$.$

Which is cheaper, buying the phone outright or the instalment plan?