That particular device works with the TO. This is of course subject to the (A/V)DSL standards adhered to/supported by the ISP.
Certainly it might be more convenient if the MOX would feature a such modem already built-in, but then it would increase the cost and thus the price and people may back away, considering that the majority would be furnished with a DSL modem from their ISP anyway.
And if such modem was built-in and the ISP would not adhere to DSL standards, which is not that uncommon, then users may want to return their Mox and/or blame the Mox team for the incompatibility, in short it could be bag of headache.
With the current modularity the user can decide whether to invest in such DSL modem via the Mox’s SFP port/module.