Android App as Service to receive and Display Messages

Hi everybody, I need this: A Android-App which is running as a service. Means: Running always in Background. Even in Sleepmode, after Reboot or whatever. Always! Once the device is connected to wifi-network, the service should receive a String from a Webserver via http-request to a php-Script every X Seconds. If the String received is "NULL", then do nothing. If the String != NULL, then Display a Notifcation on the Display with Title and Message and a Link to my other (existing) PhoneGap-App via URL-Shemes. A bit like Push-Nitification but without external Services. The notification should appear in every situation. So, if the user is within another App or the device is in sleepmode and the notification should -depending on the systemsettings - be able to play anotification-Sound and a vibration. There should be any kind of settings-Area where the URL of the PHP-Script can be defined as well as the number of Second to the next request. And optional: if the reuqst should also be done on 3G or only while wifi is connected. I need this App to be finished within 14 Days from now. Thanks in advance.I am looking forward to hear from you!