Smartphone Questions? Ask A Smartphone Technician for Answers
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What model iphone do you have?
If newer model do you have it set up with icloud?
This is the very last thing you can try, if this does not work and since you stated you do not have a backup, then you will need to manually re-enter all contacts.
Go on the iphone to settings>mail,contacts, calendar> scroll down and select "import sim contacts".
If you need any further assistance just let me know.