two questions

Rewatching it tonight, as part of my marathon leading up to 6 on Thursday night, of course.

Two things in this one that always confuse the hell out of me that I'm wondering if anyone could provide insight on. They're both from the final fight scene.

When Roman is telling Sidney about his story and Maureen's background and so on, he says "They fucked her three ways from Sunday." I never understand this. First of all, does he mean as in threesomes, or as in three kinds of ways (whether physical or metaphorical), then what on earth does "from Sunday" mean? Is this is slang phrase I've somehow never heard elsewhere? Did the incident with Maureen happen on a Sunday? I know I'm over-thinking a throwaway line, but still, it bugs me.

Secondly, the bit with the phone. Roman picks it up, presses "call Sid" then it's an incoming call. What happened here? The only thing I can think is that Sidney somehow had a phone identical to Roman's, and had the foresight to set it up? But that's far-fetched and illogical.

Please, help me.