Now and then I remember this Hyperion book by Dan Simmons where everyone had a cross-like gadget glued to their chests, controlled by a TechnoCore - a civilization of AIs, which enabled people to cast themselves through space portals. As the story unfolds, this cross-like (very nice choice) gadget is revealed to essentially enslaving them.

The story unfolds in 28th century, but it all seems have started in the 21st one.