I'm going to be REALLY brief, but here goes.
US' reserve system is based on LTO-Least Time Order. If you have 10 hours and I have 12, you get called first with whatever trips there are.
To understand its context it's important to understand that this was a complete 360' from what it used to be, which was first in, first out, or Seniority rules. Scheduling would call and you would pick, based on seniority. Now scheduling calls and you pick based on how many hours you don't have. Seniority used to mean something to reserves, now it basically allows you to choose from "what's the most inoffensive block" of days off and that's it.
The Duty day goes from midnight to midnight, which is also a change from 1500-1500. This becomes important because if you went off at 1500, theoretically you could commute home, now scheduling keeps you on a leash until midnight, shooting any hope of going home until morning. Future assignments (meaning tomorrow) still start at 1500 for reserves. If you don't get called, you're still on the hook for daily or if another future trip opens up at your LTO. Meaning if you have 5 hours and I have 6, you go and I wait. (BTW, I'm senior to you.) You stay on call for up to 6 days without any kind of release, unless you get a trip, come home and have rest. Then you go on a block of 2-4 days off and then the whole thing starts over again.
US East gets 11 days off per month. The rest of the month is unrelieved ON CALL, unless you actually get a trip. Keep in mind that the average hours during the winter for a reserve hovers around 30, so basically you live on tenterhooks for little pay and monotony. This becomes especially painful if you don't live in base, however, it is a punishing system even if you do.
EDITORIAL: NOT BRIEF.
EAST's system is a cobbled together network of left-overs from previous contracts. Valuable, but inefficient. LTO was the result of a huge concessionary contract post 9/11 and was ill-understood when it was voted in. IMHO, if US f/as had understood what they were voting for, they would never have done it, but there was a gun to our heads and frankly, no one realized what an awful system LTO was. To add insult to injury, the contract did not require the implementation of Preferential Bid, which was supposed to be used in conjunction with LTO, to mitigate its impact. US wanted the cost savings of LTO immediately, and implemented it unilaterally. At the same time, they refused to purchase the Preferential Bid system necessary to implement Pref Bid.
LTO is such a drastically inferior system to what used to exist that it is twice as painful as it would have been if you'd never experienced anything else. To make matters worse, US F/A s commute at a rate of 70%. LTO + commuting is a recipe for disaster.
There is much history involved in EAST's contract, undoubtedly it's all very confusing to WEST. The bottom line is EAST wants seniority back for reserves and LESS reserves. Reserves are about 20% of EAST f/a s and that is much higher than any other airline. Throw in the reduced winter flying, and more flight attendants end up on reserve. CA, a union scheduler (meaning she helps write the blocks) tries to chew up as much open time as possible making secondary blocks but she can only do so much.
Reserve was never fun, but you used to have flight attendants come into their base, fly their kiesters off the first 15 days and go home. It was left to the junior to finish out the month. The company didn't like this, because the top 10% of reserves got their time in, i.e. 85 hours and the bottom got about 20 hours. Now no one gets 85 hours, and everybody gets about 40 so it's cheaper for the company.
Try going back about 50 pages of this site and you'll start seeing a lot of posts about EAST reserve. There was quite a lot of discussion for a while and you would see some of the reality of the system. The discussion was more interesting before it was clustered under "AFA thread", but that was just being fair to the other groups.