I’ve spent the day googling all the leads on developing iphone apps on Windows and apart from buying a mac the most suitable route seems to be Phonegap. I cannot find out whether Phonegap gives access to all the native functionality. For example I want to access and manipulate the address book contents. I also want to be able to send text messages programatically and intercept and examine incoming text messages. It would be helpful if someone could confirm whether this can be done with Phonegap.
My understanding is that Phonegap is based on webapps but I am assuming that an app developed with it can run offline for operations that dont require internet access.
Even using Phonegap you will still need access to a mac to actually build your iOS application. This is a restriction that Apple has in place, and to my knowledge there is no way around it.
Phonegap uses a UIWebView to display your application built using HTML, CSS, Javascript etc, but this does not mean that an Internet connection is required for the app to run (so offline apps are definitely possible).
With regards to Phonegap’s functionality, details of the Phonegap API can be found on their website. Specific to your needs, I believe phonegap provides access to the device’s address book through the contacts API:
http://docs.phonegap.com/en/2.3.0/cordova_contacts_contacts.md.html#Contacts
I don’t think Phonegap provides the ability to send SMS messages itself, but many people have developed extensions to add extra functionality to their applications through plugins. The majority of Phonegap iOS plugins can found at the following GitHub repo. The plugin I think you require is the SMSComposer:
https://github.com/phonegap/phonegap-plugins/tree/master/iOS/SMSComposer