Not necessarily.
A letter signed by only one party setting forth the terms of the oral agreement may be enforceable. However, the writing, whether it be a letter or memorandum, must be signed by the person against whom you are seeking to enforce the contract.
The writing must contain all of the material terms of the contract so that a Court can determine what has been agreed upon.
Attorney at Law
Blado Kiger Bolan, Tacoma, Wash.