Cannot formate 4GB memory to FAT16 use for mobile phone samsung

If you are trying to format this card through a PC don't bother, it will not work when you install it into the phone.
If you are trying to format this card in the phone, you may find that your phone will not access high capacity type cards as few older phones do, and by older, I mean if the phone is more then 6 months old, the chances are that it will not allow access to the card.
Some phones also have an upper limit to the size of the card they will address and most will not address any card larger then 2gig..
Of course, you may also have a faulty card, even from new, some of the high density cards are faulty..
If you can get access to a smaller card (like say a 1gig), try that in your phone. If it works then you will find that your phone cannot address high density cards.
I have a camera, less then 6 months old, will address normal 2gig cards but it will not allow high density 4 gig cards which is a pain but alas, nothing you can do about it..