Markets exist where SIM locking has been prohibited for a long time (Wikipedia says Canada, Chile, China, Israel, and Singapore at least). Financing still exists in these countries.
The phone is absolutely not "collateral". The carrier does not take it back if you default (even if they could, they wouldn't be able to get anything of value for it). Unlocking is just an inconvenience that prevents enough people from churning that it lowers the risk of financing.
The phone is absolutely not "collateral". The carrier does not take it back if you default (even if they could, they wouldn't be able to get anything of value for it). Unlocking is just an inconvenience that prevents enough people from churning that it lowers the risk of financing.