The Mexican firm iFone S.A. de C.V. registered the name in 2003 to cover specialized telephone service for call centers and businesses.
Apple registered the similar iPhone moniker in 2007 for its popular mobile handset.
Mexico's Institute for Intellectual Property ruled Thursday that the two names are phonetically identical, and thus encroached on the trademark.
The institute says Mexican phone carriers must pay a fine of about $104,000 and stop using ''iPhone'' as a promotional name for their calling plans.
But Apple is not covered by the ruling, since it doesn't provide calling services, just handsets.