First, T7000 phones are not analog - they are digital phones with no display and 4 programmable buttons.
Now, if I understand the description correctly, you have five external lines that do not have unlimited international calls and one external line that has unlimited international calls. If that's the case, you want to split the 6 lines into two pools - one for NA calling (5 lines) and the other one for international calls (1 line).
To achieve that, you can simply change the configuration of Line 6 (or whichever line has the free international calls) to belong to Line Pool B and leave the remaining 5 lines in the default Line Pool A. You already have the system configured to access the Line Pool A using the access code 9. You can set up another access code - for example 8 - to use the Line Pool B. Once that is done, you'd have to instruct the users to dial 9 followed by a number for NA calls and 8 followed by an international number for international calls.
If you don't like the second access code, you could set up routing of calls that start with 011 via Line Pool B.
Now, back to the programmable keys on the T7000 phones - if you have an unused key (or a key with an unused feature) on these phones, you could program that key to select Line Pool B and let the users know that they can either dial 8 or press this programmable key when dialing international calls.