Kobe Bryant can afford a $300k Ferrari ... but for some reason, the NBA star hasn't sprung for a hands-free device for his cell phone.

Bryant was cruising down the 405 Freeway yesterday ... steering through traffic while yakking away on his hand-held cell phone ... a major no-no in the state of California.

In fact, Kobe's lucky he wasn't spotted by the CHP -- 'cause a talking-while-driving ticket usually runs around $159 for the first offense ... and $279 for subsequent violations.