Google is closer than ever to making modular smartphones a reality.

At the second Project Ara developer conference Wednesday, the company revealed its most advanced prototype yet for a modular phone, along with plans for a pilot program that will put its modular smartphones in the hands of consumers in Puerto Rico this year.

Project Ara is Google's moonshot program to create a platform of modular smartphones. The idea is for users to be able to swap out individual components, like the battery, processor, or camera, without replacing the whole device.

Google's Paul Eremenko also showed off Spiral 2, a new Ara prototype that can make a 3G phone call. Spiral 2 is based on the second version of Google's Modular Development Kit (MDK) for Project Ara, which provides a reference design for developers who want to create their own modules.

Eremenko said Google currently has 11 prototype modules but the plan is to eventually have 20-30 third-party modules available. Spiral 2's shells are customizable with high-resolution colors so each module can have its own design.

Spiral 3, the next version of the prototype expected later this year, will have 4G LTE functionality and will be equipped with improved antennas, which Eremenko said "will help significantly in performance."

"Firmware is hard," Eremenko said, adding that the plan is for Ara's modules to eventually match the functionality and capabilities of today's flagship phones.

While we've caught glimpses of prototypes, up until now Google hadn't revealed when consumers would be able to get their hands on the devices.

Eremenko said the company chose Puerto Rico as a testing ground for the platform because the country has an "incredibly diverse" population that is almost equally divided between feature-phone and smartphone users.

The devices will be available through two Puerto Rico-based carriers, OpenMobile and Claro, and will be sold through "food truck" style stores. The cost will vary based on the number and type of modules a user chooses. A global launch will come sometime after the pilot program but Eremenko said the timing for that is not yet known, as much will depend on consumer response in Puerto Rico.