Merlin had mm wavelength radar.
Wilf, I listed the three munition as most well-known guided examples. They are really well-known, while many other munitions (some of which in service) are almost entirely unknown. SAL is the most common guidance principle among the rather unknown types IIRC.

120mm vs. 105mm:
The French 120mm mortars with rifled barrel are extremely close to the 105mm, there's not much difference (except low angle fire) any more.
120mm cargo (ICM) bombs (IMI, RUAG, TDA) are in production since years (not necessarily in the U.S.). I've even found an Italian 81mm ICM bomb in Jane's (Simmel Difesa S6A2, under development in 2004, 9 bomblets).

I see a challenge to adjust the understanding and organization of mortar units due to the increased range and capability. The longest-ranged 120mm mortars are now equivalent to standard WW2 field artillery.
My take on this is that -despite remaining organic support assets- they should provide horizontal support to neighboring units as well (the majority of lethal fires should be such missions) in a kind of NCW spin-off.

@ODB:
http://en.wikipedia.org/wiki/Brandt_60_mm_LR_Gun-mortar