Depends on why you're calling.
If it's because your case is still on Initial Review, a service request won't do anything. Their response will basically be to keep waiting.
It used to be a 15 day wait for a response on a Service Request but they just recently changed it to 30. Must of been because of all the DACA Service Requests being done after hitting 6 months.
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Self filed AOS │Apps Received By USCIS - 3/18/19
│Biometrics Done - 4/11/19
Interview Scheduled - 4/24/19│Interview Date - 5/31/19│AOS Approval - 5/31/19
Permanent Resident Card Received - 6/8/19