extensions.conf:
================
...
exten => _777XXX,1,SayDigits(11111111111111111111111111111111)
exten => _777XXX,2,SayDigits(22222222222222222222222222222222)

exten => 887,1,Dial(SIP/052144694640@de-out,8,G(default^777123^1))
....

script
======
...
a.execute('Exec Dial "SIP/%s@de-out|8|rG(default^777%s^1)"' % (sip,confno))
...

cli output
==========
*CLI>     -- Executing Goto("SIP/1993028-081f9e38", "1993028|1") in new stack
    -- Goto (default,1993028,1)
    -- Executing Answer("SIP/1993028-081f9e38", "") in new stack
    -- Executing AGI("SIP/1993028-081f9e38", "/var/lib/asterisk/agi-bin/de.py") in new stack
    -- Launched AGI Script /var/lib/asterisk/agi-bin/de.py
helloARGS: ['/var/lib/asterisk/agi-bin/de.py']
ENV LINE: agi_request: /var/lib/asterisk/agi-bin/de.py
ENV LINE: agi_channel: SIP/1993028-081f9e38
ENV LINE: agi_language: en
ENV LINE: agi_type: SIP
ENV LINE: agi_uniqueid: 1196445657.0
ENV LINE: agi_callerid: 4316063e0
ENV LINE: agi_calleridname: Joerg Baach
ENV LINE: agi_callingpres: 0
ENV LINE: agi_callingani2: 0
ENV LINE: agi_callington: 0
ENV LINE: agi_callingtns: 0
ENV LINE: agi_dnid: 4694548
ENV LINE: agi_rdnis: unknown
ENV LINE: agi_context: default
ENV LINE: agi_extension: 1993028
ENV LINE: agi_priority: 2
ENV LINE: agi_enhanced: 0.0
ENV LINE: agi_accountcode:
ENV LINE: 
class AGI: self.env = {'agi_accountcode': '',
 'agi_callerid': '4316063e0',
 'agi_calleridname': 'Joerg Baach',
 'agi_callingani2': '0',
 'agi_callingpres': '0',
 'agi_callingtns': '0',
 'agi_callington': '0',
 'agi_channel': 'SIP/1993028-081f9e38',
 'agi_context': 'default',
 'agi_dnid': '4694548',
 'agi_enhanced': '0.0',
 'agi_extension': '1993028',
 'agi_language': 'en',
 'agi_priority': '2',
 'agi_rdnis': 'unknown',
 'agi_request': '/var/lib/asterisk/agi-bin/de.py',
 'agi_type': 'SIP',
 'agi_uniqueid': '1196445657.0'}
    COMMAND: ANSWER
    RESULT_LINE: 200 result=0
    RESULT_DICT: {'result': ('0', '')}
LOOK, 4316063e0@1993028 IS CALLING
4694548 was called
    COMMAND: STREAM FILE london-calling "1234567890*" 0
    RESULT_LINE: 200 result=49 endpos=66080
    RESULT_DICT: {'result': ('49', ''), 'endpos': ('66080', '')}
    COMMAND: VERBOSE "got 1" 1
  /var/lib/asterisk/agi-bin/de.py: got 1
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
    COMMAND: SET CALLERID 1993028
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
output
    COMMAND: GET VARIABLE "CALLERIDNUM"
    RESULT_LINE: 200 result=1 (1993028)
    RESULT_DICT: {'result': ('1', '1993028')}
1993028    COMMAND: VERBOSE "Location: london1" 1
  /var/lib/asterisk/agi-bin/de.py: Location: london1
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
Developers,developers,developers
    COMMAND: VERBOSE "Sips: ['004952144694640']" 1
  /var/lib/asterisk/agi-bin/de.py: Sips: ['004952144694640']
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
    COMMAND: VERBOSE "Calling 004952144694640" 1
  /var/lib/asterisk/agi-bin/de.py: Calling 004952144694640
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
    COMMAND: SET CALLERID 00442070993028
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
    COMMAND: Exec Dial "SIP/004952144694640@de-out|8|rG(default^777788^1)"
    -- AGI Script Executing Application: (Dial) Options: (SIP/004952144694640@de-out|8|rG(default^777788^1))
    -- Called 004952144694640@de-out
    -- SIP/de-out-08203298 is ringing
    -- SIP/de-out-08203298 is ringing
    -- SIP/de-out-08203298 answered SIP/1993028-081f9e38
    -- Executing SayDigits("SIP/de-out-08203298", "22222222222222222222222222222222") in new stack
    -- Playing 'digits/2' (language 'en')
    RESULT_LINE: 200 result=0
    RESULT_DICT: {'result': ('0', '')}
Finished call to 004952144694640
    COMMAND: HANGUP
  == Spawn extension (default, 777788, 0) exited non-zero on 'SIP/1993028-081f9e38'
    RESULT_LINE: 200 result=1
    RESULT_DICT: {'result': ('1', '')}
    -- Playing 'digits/2' (language 'en')
    -- Playing 'digits/2' (language 'en')
    -- Playing 'digits/2' (language 'en')
    -- Playing 'digits/2' (language 'en')
    -- Playing 'digits/2' (language 'en')
  == Spawn extension (default, 777788, 2) exited non-zero on 'SIP/de-out-08203298'