I have received my L520. The software user guide installed on the machine mentions mSATA capability.
Contrary to the information received from the online Lenovo chat rep, mSATA does use the same Express card slot as a WWAN card. When examining the slot, two antenna leads are visible. It would seem that the L520 advertised on the Lenovo site as "Mobile Broadband ready" is no different in hardware than the other models; the online "mobile" description is purely a marketing ploy. This is supported by the fact that the "mobile" conifgured model was only $50 more than than the other pre-configured model I was examining. The "mobile" config had Win 7 Pro, versus Win 7 Home on the other. During configuration, upgrading Home to Pro was a $50 option.
So, I guess I am still back to the basic question of whether I can add an mSATA drive immediately, and if so, which drives are compatible (Intel 310?)
Pending looking a my risk per Amazon's return policy, the easist way to find out might be to just try it. Apparently the Lenovo reps don't yet really know about the hardware in this machine.