I want to replace my phone with an unlocked iphone. How?

I my phone stopped charging and now i have the choice to replace it with the 150 $ replacement fee or buy a 150 dollars phone.
i want to do the latter in buying a used iphone 4 gb
how would this proccess go? If i bought an unyoked iphone?
if i bought a iphone locked to another carier?

10 pts thanks

No no no no, just take it to a local phone repair shop they fill do it fur 40-50 dollors or search on YouTube hire to fix it.

If you buy an unlocked phone then you can use it with pretty much any carrier.

A locked phone will only work with the company that it is connected to. (These are generally cheaper because of THIS exact limitation)

Before you replace the phone though what stopped. Is the charger broke or the battery no good anymore. Both would be cheaper to replace.