This paper describes an enhancement of the Enhanced-Observed Time-Difference (E-OTD) method of locating mobile phones in unsynchronized networks (e.g. GSM) which does away with the need to deploy additional network monitoring equipment. It is therefore a method of locating mobile telephones that does not require an external source of synchronization. The timing measurements from many mobile phones made within a few minutes of each other are combined to estimate simultaneously both the time offsets between the base stations and the positions of all the mobile phones contributing measurements. Experimental and theoretical results show that the method performs as well as standard E-OTD, but without the need for Location Measurement Units (LMUs).