The largest US cablecos are becoming a significant competitive threat to the telcos, especially now Comcast and Charter Communications are entering the mobile and multiplay market in earnest. The two companies are working together on mobile R&D, deployment and services, since their territories hardly overlap, and may well pool their resources in future to buy more 5G spectrum. Comcast went commercial last year with its Xfinity Mobile offering, and now Charter has followed suit with Spectrum Mobile, which also leverages an MVNO agreement with Verizon, as well as significant investment in WiFi hotspots and homespots. For now, Charter’s service is available only to existing or new customers of its Spectrum broadband offering. If their mobile businesses go well, both cablecos…