T-Mobile US is experimenting with fiber broadband by launching a symmetrical gigabit fiber service in New York City. The service is offered for a fixed monthly fee, but the prices have not yet been announced.   This service, which offers 940Mbps upload and download rates as well as a WiFi 6 router, is now being tested in selected Manhattan apartment buildings. The company is undertaking a very restricted trial with a third-party supplier to offer residential internet using fiber-optic lines from that partner rather than deploying its own lines. T-Mobile did not reveal the identity of its local partner.   The decision to collaborate with a local broadband provider is consistent with T-Mobile’s well-known practice of leasing rather than constructing fiber for its cell sites. Because T-Mobile is not installing new fiber connections but rather utilizing those that are already in place, initial expenses are kept low, and T-Mobile is…