IPhone with a physical problem: would Genius Bar send it away for repairs or swap it out on the spot?

If it matters, it’s an iPhone 4 and it’s three months out of warranty.

Its problem is that its home button needs repair—button responds only about a third of the time and you have to press it in JUST the right place.

If I brought it to a Genius Bar, obviously I’d be paying them for the repair, but my question is whether they would swap it out for, say, a refurb of its same age, or whether they would ship my phone off for repair and I’d have to be without it for days.