It's usually easiest to have your hotel arrange taxi service for you, but if you want to do it yourself, both Corozal and Orange Walk have a Taxi Association. Fares to most destinations in town are low, at BZ$10 or less, but rates to points outside town can be expensive; agree on a price beforehand.
Taxi Association in Corozal. 1st. St. South, Corozal Town, Corozal. 422/2035.
Taxi Association in Orange Walk. Queen Victoria Ave., Orange Walk Town, Orange Walk. 322/2560.