Regarding having more <sd>N</sd> tags...

Are you saying that if you have a directory file with 300 people in it, even if you only have, say, 14 of them marked with <bw>1</bw>, that if you attach an <sd>N</sd> tag to all 300 extensions, this will cause the phone to crash?

I mean, you can only assign as many <sd> tags as you have BLF keys, period?

If you have more <sd>N</sd> tags with values of N greater than the number of blf keys available it will crash Polycom phones. Empty <sd></sd> tags are okay.

You HAVE to enable presence in order for the presence feature to work, along with some other settings:

to set up asterisk for buddy list notifications (presence)
-make the following changes to the extensions.conf file
exten => 1001,hint,SIP/1001
repeat this procedure for all the other extensions that need to advertise themselves
-reload the extensions
asterisk -rx "extensions reload"
to set up polycom phones with buddy list and ready for buddy list notifications
-modify the <macaddress>-directory.xml file to look something like this (change it accordingly with the needed extensions):
NOTE: the extension the phone is using should not be on this list
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<directory>
<item_list>
<item>
<fn>X-Lite</fn> ;first name
<ln>1001</ln> ;last name
<ct>1001</ct> ;actual extension
<sd>1</sd> ;speed-dial index
<rt>6</rt> ;ring type
<dc/> ;divert contact - usually blank
<ad>0</ad> ;auto divert
<ar>0</ar> ;auto reject
<bw>1</bw> ;enables buddy watching - used to set up presence
<bb>0</bb> ;buddy block - blocks this contact from watching this phone
</item>
<item>
<fn>501</fn> ;first name
<ln>1002</ln> ;last name
<ct>1002</ct> ;actual extension
<sd>2</sd> ;speed-dial index
<rt>5</rt> ;ring type
<dc/> ;divert contact - usually blank
<ad>0</ad> ;auto divert
<ar>0</ar> ;auto reject
<bw>1</bw> ;enables buddy watching - used to set up presence
<bb>0</bb> ;buddy block - blocks this contact from watching this phone
</item>
</item_list>
</directory>
-modify the /srv/tftp/sip.cfg file making the following changes (this will enable the phone to watch the status of the other devices):
feature.1.name="presence" feature.1.enabled="0"
it should look like this:
feature.1.name="presence" feature.1.enabled="1"

<presense pres.reg=""/>
it should look like this:
<presense pres.reg="1"/>
-powercycle the phones

I did all the previously mentioned changes, the phones were advertising themselves but to watching the others
After enabling presence on the sip.conf file then restarting the phones, it all worked.

@James Le Cuirot
What did you try? Did you subscribe to a SIP-URI without user name?
I'm getting "BAD EVENT" for all SUBSCRIBE-Requests

-solved-

> but it can generate NOTIFY to SUBSCRIBEd users when REGISTER occurs and also when the client disconnects.

Can I send a Subscribe for a whole domain, let's say SIP:domain.de and get notified when any user who belongs to this domain (SIP:anybody@domain.de for example) goes online?
If someone knows this, please tell me!

I want to do this across a server via IAX2 but I don't think it's possible. The status of the server itself is reported rather than the status of the users on that server.

For phones which don't support line status monitor (ie: Asterisk's BLF function), is it possible to get this information through a webpage? Or maybe even sent to the phone's display?

I try to setup the line status monitor on my SPA942.
Asterisk handle well the status of the line but the phone doesn't show it and I don't find any information about the configuration needed by the SPA942.

If somebody has already setup thi feature on this phone please feel free to tell me :)

RFC for the rich presence standard can be found at: http://tools.ietf.org/html/rfc4480
RFC for the older presence standard (which Asterisk currently supports) can be found at http://bgp.potaroo.net/ietf/idref/rfc3863/.

I'm currently looking into adding support for RFC4480.