Two of the big four voice-based, AI-augmented digital assistants have confirmed a tie-up this week, with Microsoft and Amazon announcing that they will integrate Cortana and Alexa. The goal of these strange bedfellows is to provide better access to each platform’s unique features, and looks like an attempt to bridge the gap from the home (Alexa) and the workplace (Cortana). However, that still leaves a gaping void for both, in the shape of the mobile device where Apple Siri and Google Now hold sway, thanks to those companies’ dominance of the smartphone user experience. By contrast, Amazon and Microsoft have both failed in their attempt to create well-used mobile platforms, and are likely to need further partnerships to fill that…