Make sure that the mobile device is being connected to the HDMI Input of the TV that is labeled MHL. Make sure that the MHL input on the TV is enabled: On the supplied remote, press HOME → then select Settings → Setup or Channels & Inputs → BRAVIA Sync settings (HDMI CONTROL) → Auto Input Change (MHL).

What can I do if my phone doesn't support MHL?

The simple solution is that you need an MHL adapter supplied by Samsung. If point number 3 applies to you, then your phone doesn't use MHL at all. Google has opted to use a technology called Slimport. The Nexus 4 is the very first smartphone to use Slimport, so the adapters are not too common yet.

How do I enable MHL on my TV?

Connect the larger end (HDMI) end of the MHL cable to the HDMI input on the TV that supports MHL. Turn on both devices. From the menu of the TV, set Auto Input Change (MHL) to On so that the TV automatically switches to the MHL input when an MHL compatible device is connected.