The wiki on this is says:

"1K 1Call dedicated line"
- IMO this is a bit misleading as you get the same agents as other non- GS elites but just jump the queue over lower than 1K. There is huge variability in the competency of these agents and HUACA is therefore much easier as 1K.

Under GS: "Dedicated phone line with US-based agents; phone usually answered within 30 seconds".
- generally true but tends to be a longer wait time than 1K in IRROPS - though you nearly always get a more competent agent. I understand many GS agents are based in a Chicago office; though I guess some work from home (based on dogs barking in the background etc...). GS agents tend to be very diligent about documenting the conversation on the PNR.