I hear the phrase "I can't sing, that is why I play an instrument" way too much from instrumentalists. Granted these people do not have operatic voices, and neither do I, but to be a more efficient, and in the end a better musician, singing is a necessity.
This last year I participated in a Double Woodwind Quintet ensemble (2 Flutes, 2 Oboes, 2 Clarinets, 2 Bassoons, and 2 French Horns.) The purpose of this ensemble was not to perform (although we did) but to advance our skills as musicians.
One of the areas we worked was pitch. We each received a tuning tone CD and were encouraged to practice using it. During one of the rehearsals our director asked us to sing a line of music. If you can sing it in pitch then you will play it in pitch. Before you play a note on your flute, imagine the pitch in your head, and you will play it. It was amazing how well it worked.
Each musician should learn how to sing pitches. It doesn’t matter how you do it, note names, numbers or do-ra-me. Work with a tuner so you can hit each pitch correctly each time.