You can use sipXconfig to configure phones to answer calls automatically (without user intervention). This functionality is refered to in sipXconfig as Intercom feature. Intercom is supported only for devices that can be configured to automatically answer incoming calls. The intercom call can be initiated from any phone.
To configure intercom create a group that contains all the phones for which you want intercom enabled. You can use the usual methods of adding phones to the group (Devices->Phones drop-down, Edit Phone screen).
Once you have all the phones added to a group, go to the Intercom configuration screen (Features->Intercom).
You need to explicitly enable the intercom feature. The only parameter that you have to configure is the name of the group(s) that you want intercom functionality enabled for. If you have more than one such group use spaces to separate multiple group names. Group edit box has autocomplete functionality enabled - you only need to type the first character of the group name and select the name from the drop-down list.
You can leave the default prefix (*76) or configure a different prefix for intercom. Prefix is the way of distinguishing between a standard call and an intercom call. If you want to reach extension 200 and dial just 200 - the phone will ring normally. If you dial *76200 instead your call will be automatically picked up by the phone.
You can decide how long the phone should ring before the call is picked up automatically by modifying the Ring setting. By default, phones will ring for 5 seconds before an intercom call is picked up automatically. Even if you configure 0 seconds Ring time, the phone will usually have an audible and visible signal that the call has been picked up automatically. In case of Polycom phones you can configure that using sipXconfig in the Advanced section of Sound Effects screen in phone configuration.
Once the Intercom configuration is applied you need to restart affected services and generate profiles for all the affected phones. Quick Links on the Intercom screen allow you to navigate to the required pages. The easiest way to reprovision the intercom phones is selecting intercom group name from the filter on the Devices->Phones screen and using "select all" checkbox before pressing the Generate Profiles button.