@matigo Presumably, you could get the SIM with a phone-you-don't-particularly-want, then later on buy the phone you do want, put the SIM in it and sell the phone-you-don't-particularly-want but you'd only get second-hand value for it which would sting.
I suppose phone contracts are made for people with ordinary needs and wants. If you're not ordinary you're better of without a contract. Contracts have handy things like family plans of course but they're a kind of shackle.