Nokia 5250 - Manual (Page 35)

Warning:
When you use the headset, your ability to hear outside sounds may be affected. Do
not use the headset where it can endanger your safety.
Do not connect products that create an output signal as this may cause damage to
the device. Do not connect any voltage source to the Nokia AV Connector.
When connecting any external device or any headset, other than those approved
by Nokia for use with this device, to the Nokia AV Connector, pay special attention
to volume levels.
Your device 35