En réponse à Alexandre Lang :

>So [?] is just a pause? Or is there a difference?

There is a difference. The glottal stop exists in French only 
non-phonemically, in front of words beginning with a vowel when pronounced 
just after a pause (you get a little "click" or "clip" sound coming from 
very far in the throat). Try it. You may not hear it at first, but you do 
pronounce it for sure (it's physiologically inevitable. If you try to 
pronounce a vowel after a pause, you will necessarily pronounce the glottal 

When trying to imitate donkeys with the sounds usually transcribed as 
"hi-han", French people often put a glottal stop between the two vowel 
sounds too: [i?a~:].

I've personnally never had a problem with glottal stops and fricatives 
([ah] is really simple: pronounce [a] and carry on blowing forcefully 
without moving your mouth. At first what you'll get will probably be closer 
to [ah:], but it's easy to train it to make it shorter). Other gutturals 
like pharyngeals and epiglottals on the other hand have always eluded me...

Christophe Grandsire.

You need a straight mind to invent a twisted conlang.