Tone is not phonemic in English. What you are describing is properly called intonation, which is the application of pitch (as well as stress, loudness, tempo and other markers) to distinguish more subtle conversational functions.

Stress in English is phonemic however, viz. this minimal pair:

"rekord (record, n.) vs r@"kord (record, v.)

This is a regular phonological process in many English dialects to derive verbs from certain nouns (or is it the other way around?). Future English could turn this into a tonal distinction - I think that has a precedent in Swedish.