The Ericsson Labs team just launch their Web Location API, that is designed to provide the developer with access to the operator positioning data of mobile phones.
The API can be used in a variety of Location-based apps, enabling the application provider to offer the application user with geographically tailored solutions.
The Web Location API is supposed to help locating almost any mobile phone, since it is using the positioning systems in mobile operators’ networks.
Following is a drawing from the Ericsson Lab site that illustrates this capability:

The API has the necessary privacy protection methods, and the required permissions from the subscribers.
More information can be found in Ericsson Lab’s Web Location developer portal.