The modem IP, if it's really that good, is reason enough to justify continuing to invest in the mobile IC market. There are plenty of apps processors out there to pair it with and maybe eventually integrate it with.
Maybe it's just my bias as an old modem guy, but I think if you've got the modem, you can always find an apps processor partner to work with. But if all you've got is the apps processor and no modem, well you're just another face in the crowd.
ST has just confirmed silicon proof that the port of the ST-E NovaThor (w/ARM core) from 28nm bulk to 28nm FD-SOI boosts performance by 30% and cuts power in half (see http://www.st.com/internet/com/press_release/t3370.jsp). For a smartphone user, that should mean getting *an extra day* before you do the late-afternoon-where-can-I-plug-my-phone-in-? routine. Could this be their ace-in-the-hole? (sure wish I had one in my phone!) Plus IBS has estimated that per-die cost for FD-SOI is going to be half that of bulk planar or FinFET at 20nm (which is in very-fast-follow) http://www.advancedsubstratenews.com/2012/11/ibs-study-concludes-fd-soi-most-cost-effective-technology-choice-at-28nm-and-20nm/. Interesting times to come?