Expert advice on certificate-signing mobile applications

Hi, ? I want an expert advice on how to sign your mobile application. What I am looking for is a step-by-step guide: 1) Explanation of what features / advantages will signing the application have 2) How/where to obtain a certificate. 3) Explanation of pricing of various certificates 4) Explanation of time-validity / other licensing terms of various certificates 5) How to actually sign? the application having? obtained the certificate. I am looking for someone who can provide help for all platforms - J2ME, IPhone, Windows Mobile, others. I am hoping to get a real expert advice - she/he should 1) explain the procedure completely 2) help me achieve the objective of getting my mobile application to work without those security alerts and prompts on file system/internet / other access. Thanks & Regards, Janak