FRAND agreements try to insure that patent holders do not engage in "patent ambush" and disclose all the patents that are essential to a standard. Here is a recent situation where Motorola disclosed (partly due to the insistence of Apple) a patent as essential during the GPRS standard creation, Motorola nevertheless obtained an injunction against Apple for patent violation. This is because while Motorala would be forced under FRAND agreement to license its patent under "fair, nondiscriminatory and reasonable" terms, Apple did not seem to have made a serious attempt to obtain such a license. See FOSS Patents
(Article from Mac Rumors)
