This paper describes the use of standard LTE communications signals to perform positioning indoors, despite the difficult propagation conditions in such environments that require a number of strong signals and a wide measurement bandwidth. Experiments show that the CRS transmissions embedded in normal LTE downlink signals from multiple network operators' base stations can together be used to perform horizontal localization indoors around a building, with an accuracy of around 15m for full bandwidth LTE signals. A reference unit (LMU) is required. Alternatively and with more reference measurement units, 3D positioning can be performed using the uplink signals transmitted by the target LTE modem, and it is shown that a set of DM-RS transmissions embedded within normal uplink communications traffic to its base station can be combined to also give measurements of signals with a wide effective bandwidth.