The modem is listed as "untested" on the X60 page, so I tried to explore that a bit further.
On Windows, its hardware info is "HDAUDIO\FUNC02&VEN_14F1&DEV_2BFA&SUBSYS_&REV_0900"
Some googling confirmed it was a Conexant, device ID 0x14f1,0x2bfa that was connected as the 2nd device of the HDA bus and should show as the 2nd codec of the audio card.
However it was never detected! (which may or may not be related to ACPI tables - I don't know if they contain HDA bus info)
After reading the HDA-Intel kernel documentation, I could successfully detect it with the kernel options : snd_hda_intel.model=thinkpad snd-hda-intel.probe_mask=0x103
Basically, the current hardware tables do not expose it to the OS, so you have to boot with manual probe instead of autodetection.
The modem is then detected as:
$ cat /proc/asound/Intel/codec#1 Codec: Conexant ID 2bfa Address: 1 MFG Function Id: 0x2 (unsol 1) Vendor Id: 0x14f12bfa Subsystem Id: 0x14f10000 Revision Id: 0x90000 Modem Function Group: 0x2
Then, problem is that very codec is not supported with slmodem : https://bugzilla.novell.com/show_bug.cgi?id=244436
"Some HD-modem codecs (e.g. Conexant ones) don't work with slmodemd."
So I tried to fix hsfmodem to have it compile under a recent kernel 3.x (cf http://ubuntuforums.org/archive/index.php/t-1903439.html) but gave up.
At the moment the best option for those who need a working modem seems to get a MDC card that works, like the Si3054, to replace the Conexant MDC.
Even them, it will be far from perfect, cf https://freemor.wordpress.com/2008/05/16/si3054-and-hardy-heron-the-saga-con...
Anyway, if you want to get one, search for "Modem 3054" on ebay : you will find many ML3054. As per the specsheets, it needs revE or later to be compatible with the HDA-Intel "Azalia" interface. Basically, make sure the original computer it was pulled from used snd-intel-hda instead of snd-intel8x0m (ex: lenovo y510 is ok) and you should be good.
I'm waiting for such a card, I will let you know if the modem works, but everything indicates it should. The modem could then be indicated as "working", but it will require a blob (for slmodem compilation) so personally I don't think I'll use the modem functions, but someone might be interested.