Cross-platform mobile API — Looking for recommendations

Question

So, yes, this is probably 1000th question on the subject. However, my question is somewhat different from others that were asked about this, so please bear with me:

I am looking to develop a single mobile-app that targets the three/four popular and/or growing mobile platforms (Iphone, Android, WinPhone7, RIM). This application is an extension of an existing SaaS system that my startup currently offers. This mobile-app would provide a quick-and-simple way to view up-to-date status & chart & report information for the data that SaaS application collects. Connection to the internet is required 100%. No data entry besides username/password. App is very simple with 5-6 "pages".

In phase 1, all that would need to be supported is for user to log in, get to see current status of his data stored in the cloud, get access to a few live reports

In phase 2, I'd like to be able to offer push-notification of certain key events from my servers in the cloud

My goals are:

1) The back-end processing that generates data for reports is already written in ASP.NET MVC2. I want to re-use it. It can be exposed as either a WCF service or published on a mobile-friendly website

2) I'd like to be able to deploy the patches faster than through the official app-stores/marketplaces.

3) I cannot afford to spend a lot of resources to target three-four proprietary platforms, for an app that is auxiliary to the vertical purpose of the business. I want to develop it once for all 3-4 platforms.

4) I do not have access, nor do I want to purchase a Macbook

5) I do want to deploy thru the vendor-specific application marketplaces

6) I'd like to stay way from proprietary languages/frameworks/lock-ins

Sounds like what I need is a shell around a mobile-friendly site that can be packaged as an app. Are there existing products that can make it REAL EASY for me to do so? Will doing so, preclude me from doing push notifications in phase 2? Can anyone recommend a "shell" product that would make a wrapper around the website as well as Javascript library that would look the best across all 4 platforms. I've seen the names like Jqtouch, Jquery Mobile, etc... but not sure which ones are better for what I need.

Do I need PhoneGap? I am not 100% sure here. Can PhoneGap use online-only html/javascript pages to translate into native code or must html/javascript files be distributed with the application? I'd rather have the website itself drive the UI completely, as I can keep changing the website without various version approval processes from vendor market-stores.

Thank you for help