ok i got my zync card.
I noticed there is no credit limit.
Does this card help me build my fico score, if it display no CL?
2. Can i convert this card to another card like a blue card later or do i have to re-apply?
It helps your credit score in terms of establishing another positive tradeline with positive payment history, but it does not help your utilization because it does not have a limit. Equifax and Experian FICOs do not use charge cards in their utilization calculation. TransUnion 98 (the scoring model you can buy on this site) does, which CAN lead to an Amex charge account "hurting" your score. I put "hurting" in quotes because it's usually just a few points here or there. Luckily, most LENDERS use TransUnion 04, which, like Equifax and Experian, does NOT factor charge cards into utilization. I wouldn't worry about it, though. Just use the card as you normally would. Some have even said their charge card helps their TU 98 score. I also think that the "open" terms account helps your mix of credit if all of your other trade lines are "revolving."
You cannot convert Amex Charge accounts to Revolving accounts. It will be another application. However, COUNTLESS people have said on this board and on others that once you let your 6th statement post on your Zync card, you can apply for Blue and almost be guaranteed approval. Now, I don't want you to think that it's going to be 100%, but you'll have a very good shot at it.