Can someone please tell me what the AR max code is to warp to Birth ..

Oh, Dang. I hope you have found out how to get to Birth Island by now! But just in case you don't, it's really quite simple.
NOTE - Requires an Action Replay of some sort or you can't do it.
NOTE - It is easier to do this if you do the cheat for infinte masterballs or have just saved the one you got in the story.

1. Be sure you are not in the middle of another cheat such as the one where you walk through walls or the safari zone cheat. It just complicates the process.

2. Put the Action Replay Pack into the GBA and put LeafGreen into that. Turn on the game system with the Action Switch to the left. Go to "Management". Next, go to "Add/Edit Code". Choose "Pokemon Leaf" from the menu. Then choose "Add new code". This menu should ask for the title of the code. Title it whatever you want but just to be safe, you should type in "Birth Island Access". After you hit "Done", it will then ask for the code sequence. The Code is this:

554D9257
D0472EF8

Now that you have that entered, hit "Done" and it will take you back to the Management Menu. Now, don't get too excited and try it yet 'cause we're not done. Press "Add/Edit Code" again. Select "Pokemon Leaf" again. Then choose "Add new code". Now title this one "Doors Access". Hit "Done", and you're ready to enter the last code for this cheat:

E6A003D6
8110DDD5

Then, of course, hit "Done" to go back to the management menu. This is the part where it gets kinda tricky so pay close attention. Hit "B" button to go back to the Main menu. Select "Select Game" and of course, you guessed it, hit "Pokemon Leaf". From this menu, hit the right directional button to scroll all the way down. OMG, Look! It's the codes from before! Select both cheats "Birth Island Access" and "Doors Access". Now you're ready, hit start and the game will briefly say "starting game with 3 codes enabled".
This is the "Fun" part of getting to birth Island!
Your game will now resume as if you didn't have the action replay in at all. Select your file and start up your game as normal. Now, you will pick up from where you last saved the game. From here, walk through a door. I don't care which door you use just use one. Whoa, you should be at the place where you normally go to set sail. DO NOT ASK TO SET SAIL BACK TO VERMILION! On the Action replay pack, switch the action switch to the right now. This is very important. Now, that your switch is to the right, you have access to Birth Island. Go back through the door you came, which is the door to Birth Island!
Honestly, the only purpose of this Island is to get Deoxys. When you walk onto land, you should just see a triangle statue thingy. This is not fun. You have to move the triangle until it turns red, and you must do it quickly or it will restart. The only way to really do this is to never bump into it and run up next to it and tap it immediately.Tip - Always tap the side closest to you and you won't fail.once you finish the freaky puzzle, the Island gets woozy & Deoxys will come out and fight you. On this version, you get the Defense form of Deoxys. This is where you catch him with a master ball if you have any. Or if you don't you can battle him at level 30. Catch him or you will never be able to again. If you don't catch him, turn off the game, turn it back on with the codes and try the whole thing again. After that go to the sailor guy and sail back to Vermilion. Save and you've got it made!

Hope I helped! ~TORGAZ~

Just go look in the AR section for codes yourself.