The following recommendation is if the program should make the request over the Internet, meaning that the program can work anywhere with WiFi.
As a matter of reliability and functionality, the server should have a public IP (not dynamic) to prevent third parties forwarding (dyndns, etc.).
You can send the registration data and the requirement in the url (example: miserver.com/android/?user=xxx&pass=xxx&datarequest=xxx) and the android program will read the query result to the database.
As sending is not done through the browser, there is no danger of exposing the data, and thus operates independently of the server technology you use (PHP, ASP, JSP, etc.).
This way is faster and easier than with webservices.