So, I'm not sure that I'm understanding your question correctly... When you develop a web application in ASP and host it on a server, both mobile devices and regular computers can use that application in their respective browsers.
It's important to realize the difference between a web application that can be accessed properly on a mobile device and an application that runs natively on a mobile device.
So, if you want to build an application that is accessible on mobile and desktop devices, then a web application is potentially a good choice.
The language you choose for your web application has no bearing on whether or not you will have success in allowing mobile users to access your application.
That being said, what you probably need is a good intro ASP book and (most importantly from your perspective) a good book on mobile website development.