Joining the Gaurd/Reserve as a pilot out of college is definitely do-able, and for some reason, is the best kept secret in the world. I don't know why every guy coming out of college doesn't do it.
My grades sucked in high school due to immaturity, so the USAF Academy was out of the equation. I didn't want to do ROTC, because I didn't want to get stuck with an obligation of becoming a Mortuary Officer for four years if I didn't get a pilot slot, which were very competitive and rare. So, I decided to get the best grades I possibly could, and then apply to the USAF for an off the street OTS slot.
Well, I did get the grades. In fact, I was the valedictorian, and I did that for the purpose of being competitive for a military pilot slot after college.
For some naive reason, I believed at the time that I'd need an ATP and all kinds of flight time to be considered by the military. So, I spent the next five years fu(king around with crap CFI and 135 jobs making $12,000 per year. No car insurance. No medical insurance. No movies or nice restaurants. Phone always getting cut off. Credit in the tank. Eating a lot of Top Ramen and canned tuna.
Then I started campaigning with every Gaurd/Reserve unit in the country. It's an enormous effort, but SO worth it.
I got picked up by an AMC Reserve unit flying heavies. My income instantly increased by a factor of three, and only got better from there.
Over the years in my Reserve unit, I figured out how things worked. Here's the deal: We've hired guys right out of college with a Private Pilot Certificate. Not that they would have always been my first choice, but the thing is, no one really applies from the street. Strangely, there is little competition. It's like no one knows about this great deal. So, when a sharp and decent guy with a modicum of patriotism walks in the door, he gets everyone's attention, and gets hired.
I've seen guys get hired off the street with average grades, average personalities, and little or no flight time. You don't have to be a valedictorian or an astronaut to get hired into a Gaurd/Reserve unit. At least that's the way it was with my unit.
And I'll tell you what. I've lived both lives. I have a great airline job now, but it took a long time. I've lived the civilian aspiring airline pilot life, and it was very difficult. I've served in the military too, and the satisfaction, honor, and quality of life that has given me is immeasurable. If you have a choice, the Gaurd/Reserve is definitely the way to go.
That said, you need to ask yourself why you would join. If the answer is to eventually get an airline job, then you are doing your country and yourself a disservice. Serving is a serious responsibility and privelege. Military service is not a stepping stone to the airlines. Military service is a commitment of your heart and soul, to give your life, if neccessary, to defend your country.
Good luck with your future!