Wasn't Spock the first Vulcan in
Starfleet? What's T'Pol, then?
A Vulcan subcommander working as the
first officer and science officer on a Starfleet vessel. She's not
a member of Starfleet (and neither were Kira, Odo, Neelix, Kes, and Seven,
but they were in significant positions among the crew of a Starfleet installation).
The Enterprise-D's plaque lists
it as the "Fifth Starship to Bear the Name," making the original NCC-1701
the first. What's with the NX-01?
The plaque on the Enterprise-D (and
other Starfleet ships) also says "United Federation of Planets."
The Federation doesn't exist yet, so the NX-01 doesn't count as the first
"Federation Starship."
Wasn't the first contact with Klingons
in 2218 and not 2151? Wasn't supposed to be disastrous?
Two references to this: McCoy's
statement in "Day of the Dove" (set in 2268) that humans and Klingons had
been adversaries for 50 years, and Picard's statement in "First Contact"
(the episode, not the movie) that first contact with the Klingons was disastrous,
resulting in a policy of covert surveillance before first contact.
This is the part where it gets tricky...
...and thanks to Enterprise being a prequel, we begin a far more complex dance through semantics and references as we try to reconcile apparent inconsistencies between the show and established Trek lore.
A lot of the answers being offered seem to be predicated on the distinction between humans, Starfleet, and the Federation--the NX-01 is a Starfleet ship, but wasn't a part of the Federation; the events of "Broken Bow" are of human/Starfleet first contact with the Klingons--it's the Federation first contact that happened in 2218 and was a disaster.
The problem is, this use of semantics gets progressively iffy--the T'Pol point is logical (pun intended), the Federation Starship one somewhat reasonable (if a bit unfair), but the Klingon First Contact thing is just a load of hogwash--first contact is first contact, no matter how you slice it. The Klingons obviously have relations with Vulcans, and here we see them meet humans, so what could possibly make their first meeting with an organization of Vulcans, Humans, and other aliens a "first contact"? (Dammit, Jon, tell the Tellarite to stop sticking his snout in the gagh! It's offending our hosts!). And I have no doubt that we're going to run into a few more of these humdingers as Enterprise wears on, so how are we going to save our sanity?
Fortunately, it seems that Berman and Braga have apparently given themselves (and us) an "out"--the temporal cold war. Something's happening in Archer's time that isn't supposed to be happening (or maybe was supposed to happen all along), not the least of which being the Suliban becoming advanced and influential. Other things that our mystery man "Tempus" (a moniker I swiped from the old Lois and Clark show) has done: He's caused the premature launch of Enterprise and different circumstances under which it was launched; he's caused the addition of a Vulcan crewmember; he's caused humanity to be somewhat aware that some temporal meddling IS going on. It's only going to snowball from there.
There are three propositions here:
1) Enterprise is a true prequel, and
any inconsistencies between it and TOS-VOY can be explained away by something
other than temporal meddling--everything that happens is supposed to have
happened.
2) The events in Enterprise take place
in an alternate timeline because of the temporal meddling, but something
will happen at the end of Enterprise's run that undoes everything and restores
the proper timeline, rendering Enterprise irrelevant--everything that happens
isn't supposed to happen, and it will all disappear at the end.
3) The events in Enterprise take place
in an alternate timeline, and any future Treks will be based on that altered
timeline regardless of how they clash with TOS-VOY, rendering TOS-VOY irrelevant--everything
that happens isn't supposed to happen, but what we saw before isn't going
to happen and doesn't matter anymore.
If situation 2 or 3 are the ones that apply for Enterprise, then most (though not all) of the inconsistencies we'll run into don't matter.
Problem is, we won't really be sure about it until