Originally Posted by ebzed

Economy: Up to Q you pay for changes, T is unchangable,
S, Y changeable without payment (you might need to pay differences
from S to Y, If S doesnt exist on the flight you wish to change to).
If you are a COMM account there are good odds you wont pay for Q changes.
J Class (Bonus) changeable without payment).

Business:
D, I, C changeable without payment, on W & Z you will need to pay.
X Class (Bonus) changeable without payment.

If you take a mixed ticket, For example W & I, Even if you change only the I
you will need to pay... The "law" say the lowest segment is the one that set
changeable price.