To unlock all WiFi missions in all three modes, achieve an "S" rank in all Single-Player mode missions.

Unlock the following concept art at the "Extras" menu by performing the corresponding tasks:

CONCEPT ART - HOW TO UNLOCK
Anglo Isles - Beat the Western Frontier Flashback campaign with all "S" ranks.
Iron Legion - Beat the Anglo Isles campaign with all "S" ranks.
Solar Empire - Beat the Solar Empire campaign.
Tundran Territories - Beat the Iron Legion Flashback campaign with all "S" ranks.
Western Frontier - Beat the Solar Empire campaign with all "S" ranks.
Xylvania - Beat the Tundran Territories campaign with all "S" ranks.

Unlock the Unit Dossier for the following armies by performing the corresponding tasks:

UNIT DOSSIER - HOW TO UNLOCK
Anglo Isles - Beat the Western Frontier Flashback campaign with all "A" ranks.
Iron Legion - Beat the Anglo Isles campaign with all "A" ranks.
Tundran Territories: Iron Legion - Beat the Iron Legion Flashback campaign with all "A" ranks.
Western Frontier - Beat the Solar Empire campaign with all "A" ranks.
Xylvania - Beat the Tundran Territories campaign with all "A" ranks.

You can shoot the tanks on the title screen by pressing B.

If you're using a Fighter, tilt the nunchuck and the control stick to do a barrel roll, giving you a great opportunity to evade incoming missiles. If you're using a Gunship, point the cursor on the screen near the bottom and fly as low as you can to dodge the AA fire. If you're using a Bomber, you should again fly as low as possible to dodge the AA fire, though this is considerably more difficult than doing so with the Gunship.