Why no official documentation about how to unlock Job?

[Ruanark]

Well maybe not everyone wants to level all the classes just to fund out what job(s) will came out of it? Or more likely want to get access to their (first) favourite class most efficiently ...

Best plan: level your main class required for the job you want OR CNJ to 12. This unlocks Cure, Aero, Protect, and Raise which are useful no matter what you are. Here's a list of the jobs and the required classes/lvls:

Job = Main Class + Sub Class + Cross Class*
PLD = GLD30 + CNJ15 + MRD*
WAR = MRD30 + GLD15 + PUG*
DRG = LNC30 + MRD15 + PUG*
MNK = PUG30 + LNC15 + MRD*
BRD = ARC30 + LNC15 + PUG*
WHM = CNJ30 + ACN15 + THM*
BLM = THM30 + ACN15 + ARC*
SMN = ACN30 + THM15 + ARC*
SCH = ACN30 + CNJ15 + THM*

* = Cross class, not required to unlock the job, but the job will gain some skills from this class

[Ruanark]

And if you're curious how high to level the cross classes, here's a list of when they give their last cross class skill:

THM: 26 (SMN, SCH, WHM)
ACN: 34 (BLM, SCH, WHM)
CNJ: 34 (SCH, PLD)
GLA: 34 (WAR)
MRD: 26 (PLD, DRG, MNK)
LNC: 34 (MNK, BRD)
PUG: 42 (WAR, DRG, BRD)
ARC: 34 (BLM, SMN)

So for a SMN to have everything, they'd need lv50 ACN, lv26 THM, and lv34 ARC

[Ruanark]

And if it's easier to read this way I combined the two since I have nothing to do while I can't log in -.-;

BLM = THM50 + ACN34* + ARC34
WHM = CNJ50 + ACN34* + THM26
SCH = ACN50 + CNJ34* + THM26
SMN = ACN50 + THM26* + ARC34
PLD = GLD50 + CNJ34* + MRD26
WAR = MRD50 + GLA34* + PUG42
DRG = LNC50 + MRD26* + PUG42
MNK = PUG50 + LNC34* + MRD26
BRD = ARC50 + LNC34* + PUG42

* = Sub class needed to unlock