Wireless hotspots are permeating the globe bringing interesting services and spontaneous connectivity to mobile users. In order to enable the elderly and disabled to be fully integrated into the society, it's of paramount importance to build a pervasive assistive environment where assistive services can be automatically discovered and easily accessed with the device-to-hand across the physical spaces. In this paper, we propose a framework that can support impromptu service discovery and context-aware service provision with mobile devices in heterogeneous smart assistive environments. Different from the existing approaches, the framework requires no specialized hardware or software installation in mobile client devices, and it can automatically discover and select appropriate services based on the user profile and situation context, and generate personalized user interfaces according to user preference and device capability. To demonstrate the effectiveness of the framework, we prototyped a set of assistive services in public spaces like shopping malls, leveraging the OSGi-based platform accessible from any WLAN enabled mobile devices