In our network we use Alcatel bargain modems as the GSM backhaul. they use a a pair of copper to transmit the E1s to the BTSs. This is a very cheap and reliable solution of transmitting the E1 through local telephone lines or subsriber loops, only if the cables are stable, but we are experiencing some problems when the telephone line technicians are working at MDFs this ussually causes to disconnect the e1 accidently or they create a high bit error rate causing to detoriate the voice quality. PDH microwave transmission is mostly used but this need a lot of internconnections and a city with a lot of BTSs might be frustrating. I think point to multipoint wireless tranmission is the best way. You place a basesation at a central location with 6/4 sectored antennas and you transmit it to your BTS sides. Also there are some companies that offer WIMAX as a GSM backhaul like Eion wireless company did anyone of you used this. I wonder what you guys are using as a GSM backhaul.