On the echolibre blog David Coallier has written up a post talking about their CRM tool of choice, Capsule CRM, and some of the things they're doing to create an API interface to interact with it (including a proposed PEAR package).
we realized that we needed to integrate Capsule with some online services we have and so we built a PHP wrapper for their API to give developers the ability to place requests and use the web service as they wish using PHP. Services_Capsule is now being proposed to PEAR however you can already get the code from http://github.com/davidcoallier/Services_Capsule and start using it.
He also includes an example of how it can be used to create a new person, search the party information, update the user's information and add them to a pre-existing opportunity. There's not a lot of documentation for the package, so be ready to search through the source for some of the parameters and functionality.