Can I set the phone to make calls without a proxy (ie peer-to-peer)?

There are two ways of setting the phone to make peer to peer calls.
The first is where there is no proxy server on the system at all.  In this case:

1. set the ENDPOINT field on all of the SIP Info pages to DISABLED - do not enter any SIP proxy or registrar addresses on these pages. 
2. Make each entry on the Memories page the address of an endpoint or phone, in the form 1@192.168.1.2.  Note that the number before the "@" symbol is not normally significant* - there just needs to be a number, followed by "@", followed by the IP address of the end point.**
3. Note that peer-to-peer calls can only be made by using a memory - not by manually dialling from a numeric keypad.  All phones have at least one memory list (the OFFHOOK list).  Refer to section 5.10 for details on setting up memories.

The second way is where one or more proxy servers are in use, but you want to be able to make a peer-to-peer call if no proxy is available.  This is referred to as "failover to peer-to-peer".  In this case:

1. Set the proxy address on one of the 4 SIP info pages (usually the one with the lowest priority) to be the IP address of an endpoint, in the form 192.168.1.2, but set the REGISTRAR address to be blank.
2. If all attempts to make calls to higher priority proxies fail, the phone will attempt to place a call to this IP address as a peer-to-peer entity, regardless of what number is dialled or what entry is selected from a memory list.

NOTE: you cannot make a peer-to-peer call by entering an IP address on a numeric keypad - peer-to-peer calls can only be made using a memory dial.

*Some SIP phones may require this to be their phone number.

**Note, this could also be a FQDN (fully qualified domain name) if there is a DNS available on the network