If they are to be used in a fixed location such as a call centre, are you sure laptops are the best tool for the job?
Its just that laptops tend to go walkies, they also tend to get misused, have things spilt on them, get taken home at weekends and generally genarate a much higher number of instances and therefore have a much higher TCO than desktops.
We typically see a 5 fold increase in TCO for laptops over desktops.
If you go direct to Dell, HP or Lenovo or similar, they typically have a minimum of a two week lead time. The only way to reduce this is to go through resellers who have stock. Be careful regarding warranty when you go this route as its often different to what it is when bought directly - especially regarding international warranty.