I'm having the same issue as mentioned in comment #2. The issue occurs on incoming calls when clicking "open calling partner" while the phone is still ringing - the OpenERP debug log says following (I replaced the sensitive data with 'X' chars):

2013-06-19 15:34:23,116 5471 DEBUG ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Call get_name_from_phone_number with number = XXXXXXXXX
2013-06-19 15:34:23,127 5471 DEBUG ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Answer get_partner_from_phone_number with name = XXXXXX 
2013-06-19 15:34:28,051 5471 DEBUG ? openerp.addons.asterisk_click2dial.asterisk_click2dial: User's phone : SIP/XXXXXX
2013-06-19 15:34:28,053 5471 DEBUG ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Asterisk server = 192.168.XXX.XXX:5038
2013-06-19 15:34:28,108 5471 DEBUG ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Result of Status AMI request: {<Asterisk.Manager.BaseChannel referencing channel 'SIP/XX-XXXXXXXX' of <Asterisk.Manager.Manager connected as openerp to 192.168.XXX.XXX:5038>>: {'ConnectedLineNum': 'XXXXXXXXX', 'Account': 'XXXXXXX', 'CallerIDNum': 'XXXXXXXXXX', 'State': 'Ringing', 'ConnectedLineName': 'XXXXX', 'Uniqueid': 'XXXXXXX.XX', 'CallerIDName': 'XXXXX', 'Privilege': 'Call'}, <Asterisk.Manager.BaseChannel referencing channel 'DAHDI/i2/XXXXXXXXXXXX-1' of <Asterisk.Manager.Manager connected as openerp to 192.168.XXX.XXX:5038>>: {'BridgedChannel': 'SIP/XX-XXXXXXX', 'ConnectedLineNum': 'XXXXXXXXXX', 'Account': 'XXXXXXXXX', 'CallerIDNum': '<unknown>', 'State': 'Up', 'ConnectedLineName': 'XXXXXX XXXXXX', 'Uniqueid': 'XXXXXXXXX.XX', 'CallerIDName': '<unknown>', 'Privilege': 'Call', 'BridgedUniqueid': 'XXXXXXXXX.XX'}, <Asterisk.Manager.BaseChannel referencing channel 'SIP/XX-XXXXXXXXX' of <Asterisk.Manager.Manager connected as openerp to 192.168.XXX.XXX:5038>>: {'BridgedChannel': 'DAHDI/i2/XXXXXXXXXX-1', 'ConnectedLineNum': '<unknown>', 'Context': 'ISDN-PROVIDER-XXXXXXXXXXXXXXXXX', 'Extension': 'DEFAULTPROVIDER', 'Accountcode': 'XXXXXXX', 'ChannelState': '6', 'CallerIDNum': 'XXXXXXXXXX', 'Priority': '5', 'Seconds': '2841', 'ConnectedLineName': '<unknown>', 'Uniqueid': 'XXXXXXXXX.XX', 'CallerIDName': 'XXXXX XXXXXXXX', 'Privilege': 'Call', 'ChannelStateDesc': 'Up', 'BridgedUniqueid': 'XXXXXXXXXX.XX'}, <Asterisk.Manager.BaseChannel referencing channel 'DAHDI/i2/XXXXXXXXXXXXX-5' of <Asterisk.Manager.Manager connected as openerp to 192.168.XXX.XXX:5038>>: {'ConnectedLineNum': '13', 'Context': 'macro-main', 'Extension': 's', 'Accountcode': 'XXXXXXXXX', 'ChannelState': '6', 'CallerIDNum': 'XXXXXXXXXX', 'Priority': '6', 'Seconds': '8', 'ConnectedLineName': 'XXXXX XXXXXXXX', 'Uniqueid': 'XXXXXXXX.XX', 'CallerIDName': 'XXXXX', 'Privilege': 'Call', 'ChannelStateDesc': 'Up'}}
2013-06-19 15:34:28,109 5471 ERROR ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Error in the Status request to Asterisk server 192.168.XXX.XXX
2013-06-19 15:34:28,110 5471 ERROR ? openerp.addons.asterisk_click2dial.asterisk_click2dial: Here is the detail of the error : 'argument of type 'NoneType' is not iterable'
2013-06-19 15:34:28,153 5471 ERROR ? openerp.netsvc: Fehler :
Can't get calling number from  Asterisk.
Here is the error: 'argument of type 'NoneType' is not iterable'

More detailed info about the setup:
OpenERP-Version: 6.1 (Installed on Ubuntu 10.04 LTS)
Asterisk Server: Askozia 2.2.3-cfe