Friendspeak
(Alteration)

Range:  10 feet
Components:  V
Duration:  1 round
Casting Time:  1
Area of Effect:  One creature
Saving Throw:  None

This spell allows the caster to speak with one person at a time completely understandable by subvocalizing (whispering under your breath) the message. Who she is talking to can be changed, as long as all of the talking takes place within the one-minute time limit.
I recommend that DMs actually time the message to one minute. This will eliminate hassles about whether or not there is enough time or not to say something (like "the solution is...").

