Yes, this is possible with Snom Deskphones.

Configuration

Snom deskphones support pure IP/Peer-to-peer calls. To enable this function, configure the following settings on the phone's web interface:

• Filter Packets from Registrar --> "off"
• Listen on SIP TCP Port --> "on" 
• Network Identity Port --> 5060
• Block URL Dialing --> "on"

Optionally, you can as well turn off the Logon Wizard so that the phone no longer requires the user to configure a SIP account.

Then, reboot the device. This enables pure IP calls.

Usage

To call another IP address you have to enter it in standard format. For example: 192.168.xxx.xxx

You can also configure a function key to speed up the IP call.

• Type: Speed Dial
• Number: sip:<IP_address>

It was reported that calling from some 3rd party softphones might require the following:

sip:@ip address=""