Final answer:
The most common way to interconnect wireless LANs to an ISP's access device is via an Ethernet cable, which offers speed, reliability, and simple installation.
Step-by-step explanation:
The most common way to interconnect wireless LANs to the ISP's access device is through an Ethernet cable. Ethernet cables are widely used due to their speed capabilities, reliability, and ease of installation. Devices such as routers and wireless access points typically come with Ethernet ports that facilitate this connection. Once connected, this setup provides a high-speed link between the local wireless network and the broader internet.