As a term it doesn't get a huge number of searches:
[smartphone apps] 170
[smart phone apps] 28
some of the more searched terms being:
[mobile applications] 2,400
[mobile apps] 1,900
[mobile phone applications] 1,300
[mobile phone apps] 720
[phone applications] 720
I think more and more phones can be classed as 'smartphones' so I don't know whether the term is going to decrease in use?
Heres a few comparable sales for ref:
MobileApps.co.uk £850(Sedo Aug-09)
MobileApps.net $355(GoDaddy Jun-09)
quite cheap for those two I think...and a couple of others:
AppStore.de $1,330 (Sedo Apr-09)
MobileAppStore.com $270 (Sedo Sep-08 )