Spells (3e)

The character contacts a particular creature with whom the character is familiar and send a short message of twenty-five words or less to the subject. The subject recognizes the character if it knows the character. It can answer in like manner immediately. Creatures with Intelligence scores as low as 1 can understand the sending, though the subject’s ability to react is limited normally by its Intelligence. Even if the sending is received, the subject is not obligated to act upon it in any manner.

If the creature in question is not on the same plane of existence as the character is, there is a 5% chance that the sending does not arrive. (Local conditions on other planes may worsen this chance considerably, at the option of the DM.)