The 10 year old flip phone may work, if it's on the GSM network. (old AT&T phones are, but I am not familiar with Canadian mobile service providers.) However, there is a good chance that the phone is locked. You can unlock it yourself, if you contact the customer service department of the cell phone provider and plug in a few codes and navigate a bunch of menus. Also, if the phone is 10 years old there is good chance that you need a new battery. If all this sounds technologically daunting (and it can be), it may be a lot easier to buy a basic phone at the Digicel store in Negril for ~$20.