Nokia 6555 problems

I had the Nokia 6555 for only a few days before it started shutting off on me in the middle of calls and texts.  It would sometimes do it several times in just a few minutes.  AT&T gave me a new battery since I have the insurance plan, but that did not help.  They later sent me a new 6555 and it had the same issue.  I even tried buying a new memory card to see if mine had been corrupted in some way, but that did not help either.  I finally called AT&T and had them send me a completely different phone since I felt it was not reliable (especially since it is my only phone).  My new one (Nokia 6550) has not had any problems, but I wish I had not had all the issues with the other phone since I really liked how it easy it was to use.  The buttons were perfect for texting!  I would not recommend this phone because I gather that quite a few people are having the same issues with it.  Hopefully Nokia will figure out what's up and take care of the issue.