iphone 4 warranty ???

[gritts]

hi,i recently purchased a secondhand iphone 4 16gb & im starting to get no sim or invalid sim a lot,ive tried the tape on the sim tray etc but still does it.ive put the imei number into the applecare website & the warranty is till 18th october 2011,i have the box but no receipt whats the chances that i could get a replacement iphone ????

the phone is vodafone pay & go

and had an iphone 4 before this one & never got this fault

 

[iGaz]

If you take it to apple I don't see why they wouldn't keep to the warranty...

 

[yuan]

There are some problem,the sim is the evidence to warranty ,so you had better get a sim ,or you will can not to change another one ,but i think the Apple should be have a good assurance,and good service.......