basically... all those tools convert your asp.net or php code to the mobile programming language first... so i suggest you learn the mobile scripting laguage itself to gain total control....
What web-based are you going to do with J2ME? J2ME is for mobile based apps (downloaded and installed on the phone) Asp.net for mobile is a good choice as you forgot about the "tricky part" of which phone is requesting you the information and how you should handle it. I don't know any framework providing that for php, but if it exists, I'll be glad to hear about it.