You aren't able to dial from 1020 to 1000. In this scenario, since 1020 is the calling phone, it looks at 1020's CSS.
You said the CSS on 1020 is the local CSS, which contains the local partition (internal ext and local PSTN). That means that those are the only phones which 1020 can call. 1020 cannot call 1000 because 1000 is in the international partition, and you didn't put the international partition in the CSS which you applied to 1020.
I'm not sure what your end goal is, but typically you do your outbound calling restrictions with the CSS's like you are doing. If you want all of your internal phones to be able to call eachother, place all your internal phones in an 'internal' partition and apply the internal partition to all of your CSSs. If you want some phones to not be able to call other internal extensions, use a new CSS without the 'internal' partition in there.
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