With enterprise applications I have worked on, most of them use a RESTful mobile service tier, designed to remove having the server keep state for the application (since phones can lose connections quite easily).
http://www.ibm.com/developerworks/webservices/library/ws-restful/
Here's great plugin for Chrome you can use to test and work with RESTful web services:
https://chrome.google.com/webstore/detail/advanced-rest-client/hgmloofddffdnphfgcellkdfbfbjeloo?utm_source=ha-en-na-us-webapp-Advanced%20Rest%20Client%20Application
SOAP is another option, and is used in some mobile applications as well.
http://en.wikipedia.org/wiki/SOAP