On November 26, Joe wrote to Kate offering to purchase a farm that she owned. Upon receiving the letter on November 28, Kate immediately sent Joe a letter of acceptance. However, shortly after mailing the letter, Kate had second thoughts and called Joe to advise him that she was rejecting his offer. The call was made before Joe received the letter of acceptance. Has a contract been formed? Why?

No, a contract has not been form because the offer has been revoked

Explanation:

an offers can be terminated if there is rejection of offer by the offeree. an offer can be revoked before its has been accepted. Since the revocation is made known to Joe before the letter of acceptance reach joe. No contract has been form.

Acceptance or rejection of offer can be done orally or written. orally can be through phone communication.

the phone call can also be a form of rejection of offer which has been declared by the offeree.