First of all, let's have a refresher of Season 3 Desmond. After the turning of the fail safe key, Desmond time travelled back to the late 90s, where he ran into Ms. Hawking and Charlie. This is the first time we get a hint that Desmond is special and doesn't follow the rules, as Hawking suggests that he can change the course of time (however, he shouldn't). He then comes back to 2004, where he woke up naked outside the remains of the Swan. After this, he had what he called "deja vu", mentioning the content of Locke's speech before he even spoke it. After this, he constantly saw visions of Charlie dying, prevented it, but then Charlie heroically dealt with his fate.
DESMOND: I've tried, brother. I've tried twice to save you, but the universe has a way of course correcting and -- and I can't stop it forever. I'm sorry. I'm sorry because no matter what I try to do you're going to die, Charlie.
Now, cut to The Constant and Because You Left where we learn Desmond's electromagnetic history has made him vulnerable to the throes of time, however he has the power to affect it. So does this work with Season 3 Des? I think so.
DAN: Wait, your friend, Desmond? Has he recently been exposed to high levels of radiation or electromagnetism?
Let's start with the immediate effects of turning the key, which I see as most similar to turning the wheel. In both cases, after being exposed suddenly to a huge dose of electromagnetic energy, the characters are transported through time and resulted. The slight difference being Des' involved consciousness time travel for a spell, however they both finished with the travellers (including Locke and Eko in the Swan case) physically moving in space, waking up in a different spot to where their journey commenced. I see this as the only "logical" answer to the Deslockeko trio surviving an implosion. The implosion had mental effects on Locke and Eko as well, sending both of them on sort of "spirit journeys" by the Island. Btw, Desmond's clothes were obliterated by the sudden release of energy, suggested by his cuts and bruises when he wakes up. (Yeah, I know that's weak, comment if you've got a better theory about the nudity)
DESMOND: When I turned that key my life flashed before my eyes. And then I was back in the jungle and still on this bloody island. But those flashes, Charlie -- those flashes -- they didn't stop.
Then we move on to Des' flashes, which LP numbers as six (excluding his day in the past). I believe, fitting in with S4&5 knowledge, that these are brief consciousness time jumps that occur when something has been changed in Desmond's timeline, much like his dreamory in Because You Left. In this case, Charlie's death has been delayed everytime (Perhaps indirectly in the case of Locke's speech, or perhaps that was just a random remnant of post-discharge energy or something). The fate theme plays in here, because even though Charlie was "fated" to die much earlier, his "true fate", in service to the Island, was to deactivate the Looking Glass and communicate with Penny. So his fate was to have his first fate put off, so he could fulfill his new fate. :S
MS. HAWKING: You don't do it because you choose to, Desmond. You do it because you're supposed to.
If the future-seeing is consciousness travel, which each of the flashes do resemble, it is perfectly sound to say that Season 3 Desmond The Time Traveller does not contradict at all the future...or is that the past?