second replacement unit automatically shuts down and never opened again. can i asked for brand new replacement since it'll be my third replacement iPhone 4

Last September 13, 2011 I purchased an Iphone 4. I was told that it's warranty is good for 1 year. On may 13 2012, the sleep/wake button of my iphone malfunctioned. I immediately brought it to store where i bought the unit. They sent it to Singapore for service. 10 days after, on May 23, 2012, I received a text message from them telling me that my "replacement unit is available for pick up". Meaning that my old unit was replaced. When the customer representative and I checked the replacement unit issued to me, we saw deep scratches in front and back of the unit. I returned the unit to them because of the deep scratches. They told me that they'll return it to Singapore and will make a new report. Comes June 12, 2012 when i received a message again from them saying that my replacement unit is again available for pick up. the customer service representative and I checked the unit again for scratches. Finally the unit is clean. On June 23, 2012, the replacement unit issued to me automatically shuts down for 8 times. i quickly brought it to the store. Even their security saw the problem of my iphone (because he helped me troubleshoot it first). on the last time we tried opening it, it hanged and didn't continue to open. So for the third time, the unit is again subject for check up to see if it is under warranty. my concern is, apple is very vocal about their warranty which is "replacement".. Is there anything I can do to ask for a good unit from apple since this matter is a big inconvenience for me where in i have to provide myself another phone where i can use my number. and the worry that i might get another bad replacement unit.