Pay someone to worry about all this stuff, MaxWiFi has a good reputation in the UK at least. Stuff like the Ubiquiti Networks AirFiber can be good for getting from A-B over "relatively short" distances if you've identified another place which has really good connectivity which you can use, and if good connectivity is truly critical to the events. Obviously this involves masts, may involve permitting, and is a bit more complex than just a DSL line. It's usually possible to bond multiple DSL connections, and it's not impossible to get phone lines and DSL installed for short events either, although it does depend on the venue being willing to accommodate you. According to SamKnows the South Queensferry exchange (Dundas Castle) is supposed to have gotten BT FTTC capability from 1st March and some LLU (O2, TalkTalk, Sky) has happened, so again, talk to someone who specialises in this stuff and they'll be able to navigate "What is the least fucked up way to solve this for the event?". HTH, -Alex