I have three questions 1. I do not know how to get an SOS code. Can..

1,There a forum about SOS code, go have a look there.

2. Just battle some Pokemon and you will level up fast or if you have a cheat device then just cheat your level up problems.

3. After beating the game go back to their resting place and try to recruit them, bring just one Pokemon so that means you have 2, you and your partner.

You recruite the birds after you beat the game

1) When you die you will be asked if you want to send out a distress call.
Say yes. Next go to friend rescue,then choose get help,choose send sos mail.
You then choose whether to send by wireless connection or password. When you are sending sos mail by password,choose to send by password,
a sos password will appear. Tell someone (with Pokemon Blue rescue team) the sos password so they can go and rescue you(they need to go on friend rescue,go rescue,password, and they need to type the sos password you told them in).Then they can go and rescue you. If you are sending the sos code by wireless connection,go through the same process but choose wireless connection instead of password.

2) Do some rescue missions and hope you level up while doing them.

3) Before you recruit the 3 legendary birds you must beat Rayquaza. After you
have beat him visit the legendary birds again. If you beat them they might join
your rescue team. If they don't keep trying.

Hope I helped

Here are answers for your questions:

1. When you die, it will ask you if you want to send a distress call. Say YES. It will then take you to the main menu. Go to "Friend Rescue" then go to "Get Help". Now it will ask you how you want to send an SOS.

Pick password. It will show you a password and you can post it on the SuerCheats Pokemon Mystery Dungeon Forums. Wait a while and someone should rescue you. When they do, they should post an A-OK Mail code. Enter that on:
"Friend Rescue"--> "Get Help"--> "Recieve A-OK Mail". Once the code is correctly entered, you will be able to continue on your journey.

2. The only way you can level up faster is training. The best place to train is the Makuita Dojo. Another way is to feed your Pokemon lots of Gummis until it learns the IQ EXP Go Getter. That skill makes you recieve more EXP than usual.

3. You can recruit the legendary birds once you have beat the storyline, which means you have beaten Rayquaza and destroyed the meteorite. After that, you can go back to their "lairs" and attempt to recruit them. Here are their info:

Zapdos (Recruitment Rate 30%)
Mt. Thunder Peak 3F
Level 45

Moltres (Recruitment Rate 30%)
Mt. Blaze Peak 3F
Level 52-53

Articuno (Recruitment Rate 30%)
Frosty Grotto 5F
Level 52-53

NOTE: Articuno will not be at Mt.Freeze. He is at Frosty Forest!!! Don't worry, I made that mistake too!

ANOTHER NOTE: The birds' size are **** so only bring one Pokemon the size of *.

You recruit them by beating Raquaza(beating the game),then going and battleing them again.

Hi , I have some answers for you.

For question 1 , I think you have to go to the Friend Rescue option and click the Get Help option.
For question 2 , train at 1F of magma cavern (after save point) if you can't get there , try Mt.Freeze.
For question 3 , you must have completed the main storyline first then battle them again but you can only bring 2 Pokemon which are 1* or 1 Pokemon which is 2* , you can check their *size by at the bottom of the last page in their data. The three legendary birds are 4* size and their recruitment rates are 70% ( add a friendbow if you have any problem recruiting them for an extra 10%!)
Here's a WM for friendbow

Cilent : bulbasaur
Objective:help me
Place : tiny woods B1F
Difficulty :E
Reward : friend bow
Wondermail : ? ? 7 ? ? ? (...) ? 4 ? ? ?
+ F ? ? F 4 ? 6 K ? ? ?
The (...) actually is the 3dot thing , it doesn't have the ( )