ANYTIME you are considering a nice to have vs a need to have (phone upgrade vs say a working fridge or tires to pass inspection), its a matter of patience vs wasteful unnecessary cost (high interest rates). So, for nice to haves, take what would be the required weekly or monthly payment whatever and set it aside as if you were making the payment. If you stick to your plan you will have your phone and avoid costly interest, and if something needed comes up you will have that money instead of having to either finance it, do without, or defaulting on your phone payment. I dont mean to be insulting but if you havent been able to set aside the money to buy it up front in terms of budgeting/income vs expenses, do you really think (honestly asking this here, not a rhetorical question) youll be able to make the payments going forward without some financial hardship at some point? Financing is the mirror opposite of saving then buying, except 1 you pay almost double, and, 2 you bind yourself to payments every week. LASTLY- IF YOO GRIN, BEAR IT AND SAVE INSTEAD, by the time you have enough to buy, youll be able to buy a phone thats maybe not even out now, or at least have a new one whereas at the same point in time (if you finance) youll still be paying on a phone that will BE OLD AT THAT POINT.
Just my nine cents.