trenching for phone and power

[sunspot]

We've got overhead wiring for phone and power. We also have big trees and winter storms with strong winds. Not a great combo. So... proactively I thought I'd install underground conduits for the foreseeable upgrade to below grade service wiring. So if a storm hits and the wiring is trashed we can upgrade to underground wiring at that point.

I bought 3" pvc sewer pipe for the mains wire figuring it'd be an easy pull for direct burial cable and 1 1/4" sch 40 for the phone line. How much separation is needed/recommended between the two? I had envisioned two trenches a couple of feet apart but having dug for 6 hrs to make 5 m (I need to go 40) progress at 30" depth today I'm wondering if I can put both conduits in the same trench. I'm no stranger to trenching having dug more than my share but this ground is hellacious - rocks, roots, hardpan. If two trenches are better I'll suck it up and dig but if there's no advantage I'd be happy to save some work. Anyone?

Thanks, Greg