I've just been trying to figure this out as well. I thought the 'External ID' on the spreadsheet would allow me to use extensions for saved contacts e.g 7001 - Jo Bloggs, 7002 - Supplier etc so all I would need to do is dial 7001 if I wanted to speak with said person. It's a shame this isn't the case but would be a great feature.
I've just been trying to figure this out as well. I thought the 'External ID' on the spreadsheet would allow me to use extensions for saved contacts e.g 7001 - Jo Bloggs, 7002 - Supplier etc so all I would need to do is dial 7001 if I wanted to speak with said person. It's a shame this isn't the case but would be a great feature.