FireLance
Legend
This certainly looks like one of those rules arguments that will continue until WotC makes a definitive statement in a core book, and even then people will make their own house rules
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The way I see it, the Ride skill covers two aspects:
1. personal ability to perform "stunts" such as guide with knees, stay in saddle, use the mount for cover, perform a soft fall and fast mount or dismount; and
2. ability to guide the mount to leap, move faster or remain calm in combat, if it is not war-trained.
The ability to fight with warhorse could be interpreted to fall into either the first or second category. In the first category, it is simply the ability to make an attack even when the mount is itself attacking. In order to get the mount to attack in the first place, a Handle Animal check is required if the mount has animal intelligence (1 or 2). If the mount's intelligence is 3 or more, there is no need to make an Handle Animal check, but the rider still has to make a Ride check in order to be able to attack with his mount.
In the second category, it is the ability to direct the mount to attack and also make an attack at the same time. This interpretation would make the Ride skill more powerful as its use then overlaps on another skill (Handle Animal) and is a free action instead of a move action. Presumably, one could also use the Handle Animal skill to command your mount to attack when you are riding, but do not intend to attack with the mount. For example, a druid riding an animal companion might want to command his mount to attack but cast a spell (for which he would have to make a Concentration check) instead of "attacking with mount".
My preference is for the first, but as always, YMMV.

The way I see it, the Ride skill covers two aspects:
1. personal ability to perform "stunts" such as guide with knees, stay in saddle, use the mount for cover, perform a soft fall and fast mount or dismount; and
2. ability to guide the mount to leap, move faster or remain calm in combat, if it is not war-trained.
The ability to fight with warhorse could be interpreted to fall into either the first or second category. In the first category, it is simply the ability to make an attack even when the mount is itself attacking. In order to get the mount to attack in the first place, a Handle Animal check is required if the mount has animal intelligence (1 or 2). If the mount's intelligence is 3 or more, there is no need to make an Handle Animal check, but the rider still has to make a Ride check in order to be able to attack with his mount.
In the second category, it is the ability to direct the mount to attack and also make an attack at the same time. This interpretation would make the Ride skill more powerful as its use then overlaps on another skill (Handle Animal) and is a free action instead of a move action. Presumably, one could also use the Handle Animal skill to command your mount to attack when you are riding, but do not intend to attack with the mount. For example, a druid riding an animal companion might want to command his mount to attack but cast a spell (for which he would have to make a Concentration check) instead of "attacking with mount".
My preference is for the first, but as always, YMMV.