IS it possible to make it happen that one extension registered on cucm will use one designated analogue number connected on voice gateway?
Are you using MGCP or H.323/SIP?
If the first one then you would create seperate CSS on the phone and steer the call to RP/RL/RG using the GW.
If H323/SIP the simplest way you can accomplish is to use steering codes, i.e. prefix numbers on CUCM before hitting the GW so that proper dial-peer can be matched.
I am using h323 protocol. I jave registered one Cisco ATA 187 on callmanager and asssgined it one extension. On gateway, in voice port i have givrn connection plar (and ata extension.). So, Icoming FAX is ok. But when i send fax it goes out from any analogue number (FXO Prot) not frm that specific port from where it comes inside.
Did you do what I recommended? Did you prefix the call with steering code on CUCM to match specific dial peer on the GW?
In order to force a call from a specific device to specific port using H323 the easiest way is to "tag" the call by prefixing a digit(s) to the dialed number as it leave CUCM so that it can match a specific dial-peer. Consider an example where you use 9 as off-net access code on your cluster, so all dial-peers have destination-patterns starting with 9, i.e. 91[2-9]..[2-9]....
and they all point to common ports (circuits), if you need to differentiate one call from others you prefix another non-overlapping digit string in front. In CUCM this device would have it's own CSS pointing to dedicated Route Pattern - Route List that let's say would prefix another 9, when the call hits the GW it matches a dial peer with destination-patterns such as 991[2-9]..[2-9].... that points to specific port, you strip.