Maybe you already know about
DrGeo" from Hilaire Fernandes or Phratch for Android). Still these environments do not yet offer a deep integration into the mobile world and even commercial ST vendors do not yet offer an easy possibility to run ST code on mobiles.
Now David Buck is trying to fill this gap and is working on another Smalltalk VM for Android. Very interesting and I hope he makes good progress so that nice Android/iPhone apps built in Smalltalk will appear soon in appstores.
Read more about it here about it or listen to James podcast.