I am not an attorney. So my opinion counts for squat.
But, from what little I know, I doubt Yana could win. Yana does not have a signed piece of paper from Oliver agreeing to the the terms. Oliver's sole knowledge of the terms of the "agreement" were established in the telephone conversation.
On Sunday, in a telephone conversation, Oliver agreed to grant Yana an easement for a pipeline across land owned by Oliver for consideration of $50, Oliver to deliver a deed to the easement and Yana to pay the $50 on Friday . On Tuesday Yana wrote Oliver, "This confirms our agreement of two days ago whereby you will deed me an easement for a pipeline across your land for which I will pay you $50.00 and that you will deliver a deed to the easement this coming Friday and that I will pay you for it then." Yana signed the letter and Oliver received it on Wednesday. On Thursday Oliver phoned Yana to tell him that he'd changed his mind about the easement. Yana threatened to sue Oliver for breach. Could Yana win?
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It depends on what state really. There are some that still take a verbal contract as binding. Some however only recgonize written contracts, so yes dependant on the law of where they are at Yana could possibly win her case.