1. A handsfree apparatus coupled with a phone and allowing a handsfree phone call via the phone, the handsfree apparatus comprising: a storage medium having a database including a primary control program and a model-specific program, the primary control program being stored in a predetermined storage area for enabling the handsfree phone call when coupled with the phone, the model-specific program being stored separately from the primary control program and operated to resolve a model-dependent constraint by being incorporated in the primary control program, the model-dependent constraint arising when coupled with the phone, the model-specific program being associated with phone model information, the model-specific program being associated with program specification information to specify the model-specific program independent of the phone model information; a phone information acquisition means for acquiring phone model information and program specification information when coupled with a phone; a model-specific program retrieval means for retrieving model-specific program corresponding to the acquired program specification information from the database when the acquired phone model information is not included in the database; and a program execution means for executing the retrieved model-specific program by incorporating in the primary control program.