I haven't needed to visit a service center or call a mobile tech yet. I've owned my 3 for 17 months and 19K miles. The driver's window regulator could use an adjustment (it needs two pushes to go up) but other than that, it has been defect free. My nearest SC is 3 hours away, so I plan to stop in at the 2 year mark to change filters and change/check fluids.
As a comparison point, the past 3 new cars we bought before the Tesla were pretty good too:
2016 Chevy Volt 5 trips to dealer in the first 3 years: a software upgrade (took two trips to get it right), a faulty 'park' sensor in the transmission (two trips too, still not 100% right), one for an A/C cable recall. I'd call it an OK track record, not great. Problem compounded by Chevy dealer's lack of experience with Volts. But moderated by the fact that the dealer is 2 miles from my home.
2012 Honda CRV 90K miles, no unscheduled visits ever, scheduled maintenance only
2011 Subaru WRX Sold in 2016 with 65K miles- 1 warranty visit for a rattle in the rear seatback latch (I was picky-fixed while I waited). Plus scheduled maintenance.