Even though Apple has now filed a motion to intervene, Patrick T. Igoe, Esq., writing for Groklaw, gives his opinion on how developers should deal with a lodsys patent claim made against the iPhone or iPad app (or Android, or other platform).
However, if transaction costs rise through legitimate defenses or declaratory judgment actions, the business model is strained. Lodsys needs developers to think it is cheaper to settle than it is to fight. Developers should consider, however, whether filing a declaratory judgment action in their own district might have the possibility of creating a less costly and more satisfying resolution. With a declaratory judgment action, it is Lodsys that is faced with a dilemma. For a small or medium sized target, it may be more economically sensible for Lodsys to drop the demand for the small licensing fee even if they somehow feel they could win. It may be especially compelling if major weaknesses are identified in the infringement case, as I believe they could be here.
He also stresses you should talk to an attorney. (Of course.)