Hi Rox..

There are 4 theories to promissory liability (collectively known as the Law of COntracts):

1. Bargained for Consideration (A promise in exchange for promise or act)
2. Promise + some antecendent benefit (moral obligation)
3. Unbargained Reliance (Promissory Estoppel)
4. Form/Seal

Most often, one of the necessary elements of a contract is consideration. i.e., there is an offer and an acceptance. That is the bargain. Within the bargain, there is an exchange of a promise for a promise. i.e., the cleint's promise to pay in exchange for your promise to render software development services.

What happens when you cause a client to rely on a promise you have made. In this case, there is no bargain. Yet, because the client relied on your promise, he/she has suffered some detrement. Is this person out of luck because the reliance was not bargained for? The answer is no. Basically, the defendant in a case like this is estopped from claiming that a promise was not made. Of course, there is more to the story. If the defendant had cause to know that the plaintiff could reasonably rely on and act upon the promise, the case is that much better for the plaintiff.

Typically, if you are a lawyer for a plaintiff, you will assert a claim under as many thoeries as you can.

With all of this said, be careful what promises you make. While you may not be making a contract, that does not mean you cannot be sued for breach of promise.