Overland Flight is Not normal Flight
The rules for Overland Flight state:
Overland flight works like a fly speed with one exception: A creature can take a move action to use overland flight only if it has taken no actions that turn, except free actions or move actions using overland flight. The creature can then take only those actions until the start of its next turn. See also fly speed.
That means you can't use a standard action or minor action after using Overland Flight, and you can't use Overland Flight if you've already taken a standard action or minor action.
However, if you do use Overland Flight, you can take another move action to move your Overland Flight Speed again.
Overland Flight is not an asymmetric rule
Overland Flight works the same whether you are a PC, NPC, or creature. The most up to date rules, according to the compendium, occur in the Monster Manual 2.
I don't even recall seeing rules for Overland Flight in PHB2. I will edit this answer with further rulings if a page number is provided.
The Rules in PHB2 For Overland Flight are out of date
PHB2 on page 223, in the glossary states:
overland flight: An overland flight speed works like a fly speed with one exception: While you are in the air using your overland flight speed, you crash if you take any action other than a move action to use overland flight or a free action.
This text is quite similar to the original text in the DMG, page 48:
Overland Flight: Overland flight applies to creatures that fly to move from place to place but remain on the ground to fight. A creature using overland flight loses its minor, immediate, and standard actions while it flies, and can use its move action only to fly. The number associated with overland flight is the number of squares the monster moves with a single move action. If it takes actions to do anything else, it crashes.
The PHB2 entry is clearly a summary of the more detailed DMG rule: "While you are in the air" and "While it flies" are equivalent statements. Both state that if you take any other action then a move action you crash, though the PHB2 explicitly calls out Free actions, while the DMG implies it by stating you lose your minor, immediate, and standard actions. In addition, Glossary entries are usually summaries of existing rules: other glossary entries in PHB2 even explicitly call out the DMG for further rules. Finally, the previous section was called "Rules Updates". Since the Overland Flight rules are not updated in that section, it is unlikely this is meant as a rules update.
As such, and since the compendium only contains the rules from the Monster Manual 2, both rules have been replaced with the more up to date rules in the Players Handbook 2.