At its max optimization and only watching a portion of it, it drops down to around 3000 polys rendered per second.
This is almost half of the total polys available on the iPhone to keep good fps.
Now, is there something possible to do to reduce its resolution and polys or I must just use a simple modeled mesh?
“does it make sense”: its not supported, neither on Unity iPhone 1.x nor Unity iPhone 3.x
So the question does not exist 
Aha, so it sure it didn’t make any sense so they cut off the support totally 
OK I’ll model my terrain by hand it will be a simple one :roll: