VIBRATE STAYS ON - Samsung SPH-M300 Cellular Phone

Follow the below instructions and you can remove the vibrate state. I have included a link to download the phone's manual as a PDF file.

Sound Settings
Ringer Types
Ringer types help you identify incoming calls and messages.
You can assign ringer types to individual Contacts entries,
types of calls, and types of messages.
Downloaded Ringers can be downloaded right to your
phone.
Preprogrammed Ringers include a variety of standard
ringer types and familiar music.
Vibrating Ringer alerts you to calls or messages without
disturbing others.
Selecting Ringer Types for Voice Calls
Your phone provides a variety of ringer options that allow you
to customize your ring and volume settings. These options
allow you to identify incoming calls by the ring.
To select a ringer type for voice calls:
1. Select Menu > Settings > Sounds > Ringer Type >
Voice Calls.
2. Select With Caller ID or No Caller ID.


http://downloadcenter.samsung.com/content/UM/200708/20070824101259031_sprint_m300_ug.pdf

Unfortunately, all the phones I checked with this symptom had liquid damage.