Wow, this one did pick up- in response to a few of the items above, here are my observations from my experience changing out the base yesterday:
You need to remove the left rear trunk carpeting to access the area underneath the antenna- there are two plastic pop clips holding it in place- it's also helpful to remove the black hard plastic storage areas towards the bottom left (held down with two more clips) and the storage compartment towards the top left (where your disc changer would be if you have one- I don't).
With some wrangling, you can carefully peel back the carpeting without damaging the molded in shape of the thing a foot or so to allow access to the underside of the antenna mount. First thing you immediately notice is a pretty beefy bracket directly beneath the antenna base you need to change (dammit... so I thought).
The bracket is on with three 13mm bolts, and it's pretty quick to remove- but there's a rats nest of wiring around it and attached to it, so you can't movie it much out of the way to get at the area you need to access. Here's where the "easy" way do to this comes in...
Grab a small hand mirror or makeup mirror and look at the bottom of the antenna base, and the bracket in the way... there's actually an access "hole" in the bracket that (when the bracket is bolted back up) aligns with the threaded bolt on the bottom of the antenna base- so realistically, all you need is something long and skinny to reach up and through to the base of the thing.
I'd take pictures, but I already put the trunk back together and don't really have it in me to take it apart again. Basically, you need to get a 2.5mm hex key bit to hook up with the bottom of the threaded bolt that holds the base on.
I did this with: screwdriver w/ 1/4" sq socket head + 6" long 1/4" socket extender + sq socket to hex socket adapter + 2.5mm hex bit.
Doing this by feel, it took me 5 or so attempts before I seated the bit in the base of the bolt. Once I did, I loosened it enough to see the antenna base come loose from the rear quarter, and then carefully (and slowly) unscrewed the bolt until it was free of the old base. Keeping pressure on the bolt (so I didn't have to remove it and try to thread it back up in there), I grabbed the new base and threaded it on, tightened it down, and it was good to go.
All told, it took around a half hour. And to answer the questions about the phone b/t antenna, the hookup for the phone and the radio unit plug into a sender about the size of a playing card that's integral to the portion of the antenna base inside the trunk, so I'd assume that the b/t reception might get a little squirrely, but can't be sure since my car isn't equipped with it (early 04 model).
Hope this helps anyone who ended up snapping the bee stinger off like I did!