After some time your 3088 Dualphone doesn't make the ringtone.
You can't really use that phone anymore. When some one call you, the phone doesn't ring.
It's a common failure for this phone. The phone has 2 speaker and one microphone. You have to replace the rear speaker, the one for the ringing tone.
Here are the steps to open the phone and change the ringtone speaker.
Step 1: Open the Battery Case and Remove the Battery
Open the battery case and remove the battery.