Please I don't want to sound like a no it all, but you can configure the UC520/CME for auto-answer intercom. I have personally done it. Here is the Cisco documentation to do so.

https://www.cisco.com/en/US/docs/vo...figuration/guide/cmeinter.html#wp1011632

As far as 3rd party Voice Mail integration here is a config to interface to an Octel Voice Mail. CUE uses SIP integration, the choices for that are endless. You could also use H323 integration, Cisco has a Stonevoice integration document. Sorry I cant post pics....

Analog Voice Mail
You can integrate Cisco CME with analog systems to provide voice mail services, as shown in Figure 11-5. In general, these systems connect to the Cisco CME via Foreign Exchange Station (FXS) analog phone interfaces. Each port is configured as a normal plain old telephone service (POTS) dial peer in Cisco CME.


Figure 11-5. Cisco CME with Analog Voice Mail


Cisco CME interacts with the analog voice mail system via inband dual-tone multifrequency (DTMF) tones. All call routing and MWI information exchanged between Cisco CME and the voice mail system also occurs via DTMF tones.

When integrated with Cisco CME, an analog voice mail system provides the following:

Direct access to voice mail

CFNA or CFB to a personal greeting

MWI

Many types of analog voice mail systems are available. The Octel system from Avaya and the Reception system from Active Voice, LLC are two of the more popular models. The following sections discuss Cisco CME integration with these systems.

Octel
Integrating the Octel voice mail system with Cisco CME requires configuration on both systems. The configuration sample in Example 11-8 shows how to configure the CME.

Example 11-8. Cisco CME Configuration for Octel Analog Integration
router#show running-config
call application voice bator flash:app-h450-transfer.2.0.0.9.tcl
call application voice bator language 1 en
call application voice bator set-location en 0 flash:/prompts
!
voice-port 1/0/0
caller-id enable
!
voice-port 1/0/1
caller-id enable
!
dial-peer voice 5000 pots
application bator
destination-pattern 5000.....
port 1/0/0
!
telephony-service
voicemail 5000
transfer-system full-consult
!
vm-integration
pattern direct 2 CGN
pattern ext-to-ext no-answer 5 CGN * FDN
pattern ext-to-ext busy 7 CGN * FDN
pattern trunk-to-ext no-answer 5 CGN * FDN
pattern trunk-to-ext busy 7 CGN * FDN
!
ephone-dn 1
number 1000
call-forward busy 5000
call-forward noan 5000 timeout 5
application bator
no huntstop
!
ephone-dn 2
number 1001
call-forward busy 5000
call-forward noan 5000 timeout 5
application bator
!
ephone-dn 100
number 3000*....*
mwi on
!
ephone-dn 101
number 3001*....*
mwi off


The Toolkit Command Language (TCL) application (called bator in the preceding configuration) is used to support a hookflash operation on the FXS ports. FXS port 1/0/0 is used for voice mail access, so the POTS dial peer points to this port. Port 1/0/1 is used for MWI operation.

The series of vm-integration commands specifies the DTMF digit strings to be generated to the analog voice mail system to control feature operation, such as selecting which greeting (external or internal, or busy or no answer) to play to the caller. The MWI DNs have asterisk delimiters surrounding the wildcards that match the extension number for which MWI must be turned on or off.

Note the following restrictions when integrating an Octel system with Cisco CME:

One FXS port must be dedicated for MWI operation.

The Octel system must have analog ports and must be configured for analog DTMF integration. Digital and Simplified Message Desk Interface (SMDI) integration with CME is not supported.

The Octel system does not distinguish between extension-to-extension and trunk-to-extension transfers. Thus, you must configure the DTMF patterns for these transfers with the same values on the Cisco CME system.

The MWI ephone-dn must use the . wildcard rather than the T wildcard to specify the exact extension length. Also, you must use an asterisk before and after configuring the called party ID (for example, number 3000*....*).

Active Voice Reception
The Reception system from Active Voice, LLC is another popular voice mail system. To allow calls to be forwarded to the Reception system, you must configure Cisco CME with four different DTMF patterns for the following four possible call flows:

Extension-to-extension no answer

Extension-to-extension busy

Extension-to-trunk no answer

Extension-to-trunk busy

When the Reception system receives the DTMF pattern, it plays the corresponding voice mail prompt.

Example 11-9 shows how to configure Cisco CME to work with the Reception voice mail system.

Example 11-9. Cisco CME Configuration for Reception Analog Integration
router#show running-config
voice-port 1/0/0
caller-id enable
!
voice-port 1/0/1
caller-id enable
!
dial-peer voice 5000 pots
application bator
destination-pattern 6800.....
port 1/0/0
!
telephony-service
voicemail 6800
!
vm-integration
pattern direct 2 CGN *
pattern ext-to-ext no-answer 5 FDN * CGN *
pattern ext-to-ext busy 7 FDN * CGN *
pattern trunk-to-ext no-answer 4 FDN * CGN *
pattern trunk-to-ext busy 6 FDN * CGN *
!
phone-dn 2
number 3002
call-forward busy 6800
call-forward noan 6800 timeout 10
!
ephone-dn 25
number A1.....*
mwi on
!
ephone-dn 26
number A2.....*
mwi off