You can stay frost and raid just fine. In fact, there are ways in which you'll raid better as frost, despite the "fire is the best dps and that's all that matters" orthodoxy.
For one thing, how long will it take you do replace your shadoweave gear if you respec? Do you have the spellfire set sitting around along with comparable quality shoulder and boot pieces? If you gain a little dps in changing spec and lose a huge amount of dps in changing gear, you're not helping anybody.
Further, mages almost never simply stand still and chain cast spells. Raids involve moving around for almost everybody on almost every boss fight, and they usually involve everybody, not just the tank(s), taking some damage or having to deal with distractions.
Aside from the unavoidable theoretical limitations imposed, this means that awareness and reaction speed in each encounter will make a much bigger difference than talent spec. So, for that matter, will compensating for latency, e.g. by using the Quartz mod and "/stopcasting" macros (the latter no longer being necessary when 2.3 comes). These factors don't make frost better; the point is simply that before you worry about your spec there are more significant things you might be able to improve.
There are many fights where being able to ice block (out of garrote, holy fire, demon chains, randomly dropped aggro, etc.) helps the raid a great deal, as everybody saves considerable time that might have been wasted on cleansing you, keeping your health up, pulling targets off you, or killing extra things. And, of course, dead dps is no dps.
For small scattered damage in some fights (both to save healers' focus and to avoid pushback), Ice Barrier can be worth keeping up, and it's more mana-efficient than Mana Shield, espeicially as the first one is free if you pop it and immediately drink right before the pull.
Frost also does better in damage / threat. While that shouldn't usually be the limiting factor, it can sometimes be an important consideration.
Moreover, you have to be realistic about how you'll be spending the whole of your time. Even somebody whose sole interest in the game is raiding does not spend all game time in raids, as farming gold for consumables, at the least, is necessary. If you have the cash to spec back and forth all the time, go ahead. If not, keep in mind that frost can make solo world farming and 5-person instances easier.
If you are smart and alert, minimize computer issues holding you back, and use your elemental, trinket, and cold snap cooldowns properly, you may well clear Karazhan on top in dps with a frost mage.
If you're curious how different options compare numerically, http://tc.awenet.com/index.php is a handy page.