Probably there won't be any built-in NTRIP functionality anytime soon. Using corrections via NTRIP for Trimble devices was part of the GPScorrect extension for ArcPad. In ArcGIS for Mobile you may have something similar to it in the Trimble Positions Mobile Extension by the quick look of it. There seems to be a toolkit too, so you might be able to integrate the needed functionality using it with the SDK for ArcGIS for Mobile.
Your other option is if receiving NTRIP corrections is supported by your GPS receiver's firmware, so there won't be any need for a 3rd party NTRIP client. Usually these are survey-grade level receivers but you may have the functionality in the upper echelon of MGIS receivers. (It was a while ago I worked with them but the Geocollector series never had functionality like that.)
It's probably best to contact your local Trimble distributor, they should be able to provide you with more information on what your options are.
