Improved Cooperative Metamagic( Player's Guide to Faerûn, p. 136)
Your ability to enhance an ally's spell during casting is expanded.
You can use your cooperative metamagic ability to apply the Silent Spell, Still Spell, or Quicken Spell feats to your ally's spell. If you apply the Quicken Spell feat to the spell, both your action and the caster's are free actions. You must still ready an action to use this ability when your ally begins casting, but you can ready a different standard action as well. In addition, you can use your cooperative metamagic ability an extra two times per day.
Without this feat, a character cannot use cooperative metamagic to apply the Silent Spell, Still Spell, or Quicken Spell feats to an ally's spell.