New iPhone 4s randomly shut off

Hello everyone,

I purchased a new 16gb AT&T iPhone4s a few days ago and today when I went to use my phone I noticed it had turned off by itself.  The only way I was able to power it back on was to hold the home and power buttons at the same time.  I did a lot of research on the problem and saw that if the Diagnostics had a panic.plist that there are hardware errors or failures involved.

So I looked at my diagnostics and can confirm there are two logs with the panic.plist header.  panic(cpu 0 caller 0x8007617c):lck_mtx)lock():mutex (0x9B5A2820): 0x000080000.  The phone came preinstalled with OS 5.1.

So I am here to ask if this is a case where I have no choice but to replace my phone...  From everything I've read it seems to be the case, but I've only had the phone for a few days and would be really upset if this were the case.  I gave Apple a call and they said to basically not worry about it unless it happens again...  but after doing the research it has just got me more worried.

If anyone could give me any input it would be much appreciated,

Thanks.