Arguably, this is the feature that makes a business phone system powerful. Ring-U automatically configures “soft” and physical key functionality on all Grandstream phones that support it (GRP2135, GRP2170, GXP2614, GXP2616) HTEK, Polycom VVX600, and Atcom phones with a layout similar to the one in the picture.

Parking a call in a parking slot allows it to be picked up by any phone on your system, including the one which parked it.
While on a call, press the button labelled Park 600. you will notice Slot 1 or Slot 2 turns red.. The call is now parked in that slot. It can be answered from any other phone by pressing the button with the red name beside it.
*Phones without BLF keys can park a call by transferring it to extension 600. The system will announce the slot number it is parked in back to you.

Ring-U typically configures 2 slots to display. There are 9 available slots (601-609) for a call to be held available for any phone on your system to pick up.
Place a call into the slot by parking it (see above). Pick that call up by pressing the BLF button for the slot that is red/occupied.
*A phone without keys can pick up a call by dialing the slot number. Example: The receptionist yells “Steve is on 602.” Using a phone without BLF keys, simply dial 602 to pick up the call.

Following the standard Park/Parking Slot BLF's, the display will list your other extensions, as well as their status (Green for available, Red for in use). In the photo above, the Lab extension is red because it is currently in use.
On some phones, you can one button transfer an active call just by pressing the extension.
On others you press the transfer button (typically an arrow pictoglyph) and then the extension to transfer to.

If you are configured for more phones than will display on a single page, the arrow/next keys will toggle pages. Certain phones/firmware will display an “Active” page (note the red A in the photo) of active/in-use phones.

It is possible to add BLF (Busy Lamp Field/Monitoring) and Speed Dial functionality via the customer portal that is automatically added to one, or all phones. Use the Configuration > Keys menu. In this example, a Speed Dial to open a door with one button press, was added via the Ring-U customer portal and was added to all phones automatically. Note the difference in icon beside the speed dial is a blue phone, whereas extensions display as little green people.