Flight Rules VFR IFR

[MichaelSmith]

Hi,

Novice question. In commercial aviation who decides on a flights use of VFR or IFR Aircraft ?
I believe, and correct me if I'm wrong, once decided upon it can not be changed mid-flight regardless of weather conditions.

Any help will be apprecited.

I didn't find the right solution from the Internet.

References:
http://www.airliners.net/forum/viewtopic.php?t=1345175
Teaser video production

Thank you.