Unequipping your shield is a standard action, according to the Rules Compendium's section on Shields (p267):
To use a shield, a creature must strap it to the forearm. Doing so is a standard action unless otherwise noted. Removing a shield is also a standard action.
Unfortunately, this means you won't be able to use a standard action for an attack in the same turn unless you spend an action point.
Once your shield is removed, your options are these:
- Drop your shield (free action), equip your weapon (minor action). If you want to attack, spend an action point for another standard action. This, however, risks someone else stealing your shield if you leave it unattended.
- Stow your shield (standard action), and equip your weapon (minor action). That's a second standard action! You'll need to bust out action points to make this quick, or prepare yourself to use this method over the course of two turns.
I'm not aware of any feats to speed up this swap!
Getting the shield back after dropping it
If you do #1, you'll need to recover your shield at some point. Picking something up is a minor action - this does not equip it. Once it's in your hand, it will take a standard action to either stow it away on your back (or somewhere out of the way) or equip it. Being a shield, it seems you can't simply stow it away as easily as other items, which normally take a minor action.
Where is this all from!?
This is sourced from various excerpts from the Rules Compendium's explanation of a Standard Action, particularly these sections:
- Equip or Stow a Shield (standard action)
- Draw or Sheathe a Weapon (minor action)
- Drop a Held Item (free action)
- Pick Up an Item (minor action)
- Retrieve or Stow an Item (minor action)
You should pick up that book, since it contains the most recent version of all of 4e's rules, complete with all errata and updates released since.
Best Answer
Your weapon can be a shield. And that shield can have spikes on it as well. It smells of stupid at first as trading a weapon attack for a shield AC bonus which in turn is traded for a shield bash attack sounds ridiculous.
I can't find a rule that says adding spikes on your handaxe-shield-thing makes it deal extra damage through regular handaxing. When I think about it, if such a feature existed, it would just allow you to spikify your weapon without the shield nonsense anyway.
But you may have some cool shield-related feats, especially useful if your spiky-shield-weapon is on your off-hand!
Improved Shield Bash allows you to trade your off-hand weapon for a weaker shield bash attack and a shield ACbonus.
Shield Slam lets you perform a free bull rush maneuver with every shield attack
Bashing Finish gives you a free shield bash if you score a critical.
Now, assuming you really want to have a two weapon fighting character that has shield-based options but you don't want to let go of your desired weapon, you can turn it into a shield. Adding spikes would just let you be a bit more dangerous when in defensive mode.