Does your mouth have to be wide open always when you are singing?

no. you have to close and open your mouth different amounts depending on the notes you are singing, the words you are singing, and what kind of sound you want to produce. :)

well if u sing with ur lips close to shut it sounds muffled & u can't make out the words.

make sure u drop ur jaw so you can project ur voice father...

no, not all the time. i took voice lessons and my teachers said that it helps to open ur mouth wider when u sing cuz it makes ur notes more clearer. when u cloze ur mouth it does sound more muffled.

no.
when we sing low notes ( where we can get away with almost talking) or in the middle range, we need only open our mouths comfortably. Opening up gives us the possibility to give high notes the space they need inside the mouth and pharynx ( back-of-the-mouth) to take on resonance and gain quality.
Obviously, if you have your mouth shut, you're not going to get much sound out! So, yes, some opening is necessary, but only what fits to the tone level.
It's good to keep your lower jaw relaxed enough at all times so that your molars never touch, but you don't have to go around, looking like the village idiot with his jaw flapping open.

Not really. The reason many people believe that is because they see that on music videos where the singers are lip-synching the songs. I've seen many performances where the singers were singing live and they don't open their mouths that wide nor do they make exaggerated facial expressions like they do in music videos.

No

~Music Resource~
http://www.squidoo.com/music-resource

If you take a good look at the best singers, their mouths are never wide open.