Okay, I've been reading until my eyes are crossed, lol, and this seems to be what I have found the most:
Too much calcium lowers magnesium levels. Not enough magnesium makes calcium less absorbed (apparently, magnesium works on other vitamins -vit. D and vit. C, one article said- that help the calcium be absorbed), and cause the calcium to be distributed in soft tissue, and not so much in bone (think calcium deposits, bone spur type of things). So- it is the <b><i>ratio</i></b> in which you take calcium and magnesium that is important, and that yes, they should be taken together.
Too much calcium makes for the magnesium not being absorbed as well, which makes for improper/inadequate amounts of calcium being asborbed, and improper disbursment of calcium causing soft tissue deposits...
More magnesium vs. calcium= higher blood levels/absorbtion of both; more calcium vs. magnesium leads to lower levels of both...
2 to 1 seem to be the ratio that magnesium and calcium should be taken in that keeps popping up...
Oh, and chocolate has a high magnesium content, (with some calcium), and it is suspected that is why some women crave it during pms, because magnesium levels drop during that cycle! Ha! Vindication! lol