Valve not planning to make games for mobiles, yet
Valve has emphatically stated that they will not be moving into mobile games and certainly will not be adapting their Source engine for smartphones.
The Half-Life and Steam developer has stated that they currently have no mobile strategy and Gabe Newell seems slightly dismissive of mobile gaming just now.
Newell told Develop: "On mobile we've done nothing. If people want people to build a mobile engine today, call [Epic Games CEO] Tim Sweeney."
He did praise the work that Epic have done on mobiles so far with Infinity Blade showing just what mobiles can be capable of. If we remember Newell was also very dismissive of the PS3 and now Steam support has been integrated with PSN on Portal 2.