It isn't recommended you stay on prednisone for extended periods of time unless you have to, but that's how it kind of is for most asthma steroids. I haven't heard of having to take calcium supplements while taking the medication, that's a first. I would probably take the steroid as long as the doctor says and if it helps, it helps. I've taken it without issue and remember it helping.
What's your regular medication? Remember that you have lots of options and it's possible there is one out there for you that will work well enough that you won't need extra prescriptions for when you're sick and what-not.
I've done Flovents, Foradil and now I do Advair which I like quite a bit -- it has a built in steroid.
i've been on prednisone 80mg for almost 2 months for my asthma, my doctor hasn't mentioned calcium supplements but I do take a multivitamin on a daily basis.
Short term ocasional use of prednisone in that dose should cause no problems whatsoever. You won't experience thinning of the bones on that protocol. Long term daily use of prednisone is another story entirely.