You may not think much about the small elongated cylinders or boxes perched on rooftops or street lights. But those small wireless facilities, dubbed small cells, are the building blocks for 5G, an ultra-fast wireless technology that will quicken the things you do on your cellphone and unleash a new generation of devices.

5G won’t roll out to much of Southern California for a few more years, but companies such as Verizon and AT&T are beginning to install the necessary infrastructure, including those small cells pole by pole, across the region.