What's ETF?
Early Termination Fee. That's effectively what that £487 charge is. It might just be an American mobile carrier term, apologies, but the intent is the same no matter the carrier and country - to put a hidden price on "free" phones/features/etc. and dissuade people from leaving.
Of course I worked out the actual upfront figures. I was hoping to find out if I had overlooked something - if it was worth just sticking out or if investing the difference each month would yield a bigger net gain
Nope, and nope. You'd need at least a solid 10% return on investments just to break even with the £25 penalty. A generous average return of 4% wouldn't even give you a solid £10 over the course of the 11 months on your savings.
Sheer logic alone also states that less money invested = less interest paid back. The interest earned on a single lump of cash invested at the start of a year will be more than the (nearly) same amount of cash when broken into eleven equal pieces and invested piecemeal one month at a time across the same year.
From a financial standpoint, the numbers are at best a wash.
This is clearly hair splitting territory, you're putting way too much thought and effort into justifying the difference of pennies in the big picture. If you want to stay,
stay. If you want to leave,
leave. It's a personal judgment call, not a financial one... and to that end, nobody here can even evaluate and give feedback on carrier choice because you haven't even mentioned who you're currently with, just that you're looking to switch to Three.
It's great that you're saving money! It's great that you're scaling back and want to spend less on services! What's not great is agonizing over the financial end of something that basic math has already shown to be peanuts. Stop sweating the magic of compound interest on less than £25 worth of money on a £600 financial commitment and focus on what really matters - your quality of life.
