[Asterisk-Users] G.729 confusion

[hkirrc.patrick]

dear telecom gurus,

g.729a, g.729b and plain old g.729;  are these all different?

some phones e.g. lanphone 101 says it has g.729a and g.729 (with neither 
"a" nor "b")
http://www.welltech.com.tw/products-11e.htm
is there a g.729 without "a" or "b" and different from g.729a and g.729b?

x-pro comes with g.729 (i think) also, not sure about "a" or "b" or 
neither or both?

still other phone spec has g.729ab, is there a g.729ab codec? or that it 
supports
both g.729a and g.729b?  and does that mean it does not support g.729 
without
the "a" or "b" and does not support g.729ab?

digium sell a g.729 license, does this mean it does not support g.729a 
or g.729b or g.729ab?

i have to set up a conference room and calls will be coming in from TDM 
channels as well
as sip channels.

thanks in advance,
patrick