Frontal Aviation never used MiG-31. It was and is still used by PVO ( anti aircraft defence command). Frontal aviation means in russian military jargon ground support aviation and as such operates fighter bombers, attack aircraft and helicopters.
Mig-31 is Defensive interceptor. Russia used it coz they need to cover a lot of ground ,on long distances (same as Australia right?) and izrael pilots soon they get off,they r in Lebanon for exsample. Main advantage of Mig-31 is enormus speed and climb rate. About NATO agression on Yugoslavia (yes it was agression,coz security council did not agree for action,and it was not under UN, purely NATO members participated, except Greece as i remember) for 72 days they killed more civilians then troops. Destroyed more civilian objects then army objects (except empty baracks). When is best Serbian defensive weapon "Goa" dated from early 60's ,and radars maden from microwave ,we done good. Just try to find how much NATO stated to destroyed from Yugoslavian army,and how much was destroyed. They was fooled as scool girl on first date
ROFLMAO If you go into tehnicalities and read the after war analises and conclusions of official western/NATO/US sources you will see that some of them realy pose a question: "Why on earth did Slobo capitulate?" Back to the topic: Perhaps they are buying the MiG's and Su's also for one other reason. Namely this buys have quite a few less strings attached to them if you try to buy modern equipment from west and especcialy from US. For all SU lovers (good shots of vector thrust in action); http://marcbrecy.neuf.fr/valse.html
Simple,casulties on Serbian side will be huge in case that NATO go ground offensive,in troops and civilians. Serbia did preserve capability of army,but we was no match in equipment and number for NATO. But one is clear,that groud assoult woud be devastating to nato troops allso.
Also Serbia knew the game they had been playing for years was up (neighbour bullying that is) and if they were to have a future as a civilised, accepted and prosperous part of Europe (EC or otherwise) they would have to stop. As it stands now Serbia may look forward to a brighter future.