tuxsavvy, thanks for this valuable and very informative post.

As for Hirose U.FL, they're indeed ones I'm referring to. This page:
http://wiki.maemo.org/N900_Hardware_Hacking
...contains invaluable info about possible solutions and commonly available adapters, that one can use for connecting (see "external antennas" part). There is also note about FMTX contact pad (*not* H. U.FL), and it seems it's just connected by spring-like "clip".

This page seems to confirm that (clip for FMTX):
http://wiki.maemo.org/N900_FM_radio_transmitter

Overall, it's possible to - relatively easy - extend range of GSM, GPS and WiFi/Bluetooth (same frequency range = same connection pad). If I'm not wrong here, Bluetooth should be also connectable via headphone jack, due to it sharing same chip as FM radio (with antenna shared with headphone jack). Of course, that would require specially crafted DIY connector with jack plug.

As for Hirose U.FL, it's commonly used in mini-pcie cards, found in notebooks/netbooks/UMPC/some bigger tablets. So, cables for them, are - novadays - also quite common, so instead of buying adapter, one can craft one (with due care, cause it need to be shielded correctly - such thin cables are capable of catching interferences).

To be honest, it's so (relatively) easy, that I'm 100% sure I'll do it one day - only one thing that I need it's time Mugen Cover (that I use daily, alongside DIY dual-scud battery) got enough room for all adapters, so no need to werar&tear H U.FL.

/Estel