На Cisco делаем следующее

voice service voip 
 allow-connections h323 to h323
 allow-connections h323 to sip
 allow-connections sip to h323
 allow-connections sip to sip
 redirect ip2ip
 sip
  registrar server expires max 3600 min 3600
  redirect contact order best-match
  no call service stop

Делаем преобразование номера (убираем префикс 70)

translation-rule 70
 Rule 0 700 0
 Rule 1 701 1
 Rule 2 702 2
 Rule 3 703 3
 Rule 4 704 4
 Rule 5 705 5
 Rule 6 706 6
 Rule 7 707 7
 Rule 8 708 8
 Rule 9 709 9

Описываем куда будем отсылать звонки если наберем префикс 70

dial-peer voice 116 voip
 corlist outgoing call-longdistance
 destination-pattern 70...
 progress_ind setup enable 3
 translate-outgoing called 70
 session protocol sipv2
 session target ipv4:XXX.XXX.XXX.XXX:5060
 session transport udp
 dtmf-relay rtp-nte
 codec g711ulaw
 fax rate 9600
 fax protocol pass-through g711alaw
 clid substitute name
 no vad 

где XXX.XXX.XXX.XXX - Asterisk

sip-ua 
 authentication username <USER> password <password>
 nat symmetric check-media-src
 retry invite 3
 retry response 3
 retry bye 3
 retry cancel 3
 retry options 0
 timers trying 1000
 sip-server ipv4:xxx.xxx.xxx.xxx

где xxx.xxx.xxx.xxx - Asterisk, <USER> - авторизация на Asterisk-е, <password>
- пароль на Asterisk-е



На Asterisk

<users.conf>
[DO2]
allow = ulaw
context = DID_DO2
dialformat = ${EXTEN:1}
hasexten = yes
hasiax = no
hassip = yes
host = yyy.yyy.yyy.yyy
port = 5060
registeriax = no
registersip = yes
secret = <pass>
trunkname = Custom - DO2
trunkstyle = customvoip
username = <user>
disallow = alaw,gsm,ilbc,g726,adpcm,speex,lpc10,g729
md5secret = <md5_pass>
insecure = port,invite
canreinvite = no

yyy.yyy.yyy.yyy - Cisco
<user> - пользователь
<pass> - пароль
<md5_pass> - пароль в MD5

<extensions.conf>
DO2 = SIP/DO2
[numberplan-custom-1]
plancomment = DialPlan1
include = default
comment = _2XXXX!,1,default,standard
include = default
exten = _02XXX,1,Macro(trunkdial,${DO2}/${EXTEN:2})
comment = _02XXX,1,DO2,standard

[DID_DO2]
include = default
include = default
include = default

[numberplan-custom-2]
include = default
plancomment = DialPlan2
exten = _2XXX!,1,Macro(trunkdial,${trunk_1}/${EXTEN:0})
comment = _2XXX!,1,d1,standard

рестартуем Астериск. 

При наборе префикса 02 с Астериска будет производиться проброс на Cisco. 
При наборе 70xxx со стороны Cisco проброс будет производиться на Asterisk. 
Для упрощения конфигурирования, можно воспользоваться утилитой asterisk-gui 
(/usr/ports/www/asterisk-gui для BSD like ports)