I'm using Field One. It runs as a Windows service on an SQL server so you only have to open a couple of ports on the firewall and you can have secure remote access anywhere you have an Internet connection. I have laptops in the vans with 3G cards so the schedule stays real time for the office and the techs. If the office adds a call, it shows up right away, techs do invoicing and billing (including processing credit cards) on site and tech status is always current so the office knows what's going on. It also integrates with QB if you want it to but I don't use that feature of it. I believe they have both purchase and monthly leasing options, we just bought it though.