Samsung Omnia i910

I have had Omnia over couple of months now. Since I am always busy, I couldn't find a time to figure some of here and there few irritating errors I have been getting when using the phone.

Here are some lists. Please let me know if there is something wrong with my phone.

When on the phone for a while, sometimes the phone dials out #min middle of a call with someone. ??? When using the phone, the screen is always blocked and goes blank. I don't know how the hell it calls out #min to verizon time to time.
My device gets very laggy. I have to turn off and on to recover it. Sometime, on/off button does not even respond. I have to literally pull out the battery to reset.
Ok. Another major error I have is when I set my phone on vibrate or silent by clicking the speaker icon, it does not work. I am often in the meeting that I need my calls to be slient. It rings all the time??? I even went to the setting and set incoming calls to slient. It still rings. Any idea???
Alarm does not work. It does not make an alert sound.
Is it a defect? I did not purchase the protection. If it is a defect, how do I go about getting an exchange?

Thanks for your expert helps.