Office-A PIX
route inside 10.10.10.0 255.255.255.0 192.168.101.x (where x is the ip of the telephone system)
Office-A Telephone system
add static route to the 192.168.120.0 network pointing to the inside IP of Office-A PIX(however that's accomplished with the system)
Office-B PIX
add the 10.10.10.0 network to the acl used to exclude NAT and the ACL used to specify interesting traffic for the crypto map. For example, if you are using
nat (inside) 0 access-list 101
crypto map your-map-name match address 101
then add
access-list 101 permit ip 192.168.120.0 255.255.255.0 10.10.10.0 255.255.255.0
If this doesn't move you in the right direction, it might be helpful if you would post a copy of your pix configs.
Bob