Process to migrate to small IP address block?

[#1]

Hi all,
I'm currently researching a need within our organisation that would need an additional static IP address (we currently have 1).  I've seen that it is possible to request a 4 address block, but would appreciate if someone could outline the process/timeline etc.
Would we need to change our existing address? etc
Thanks in advance,
Anthony

[#2]

Hi tatser,
As long as there's a justification for needing the 4 block that's not a problem. The allocation can be done over the phone and only takes a minute or so, so we can add this as and when you need. It is going to result in a new range of IP though, so ensure you're ready your side first and let us know. Once added the new range would be picked up with a reboot of the router.

[#3]

OK, a few things you need to be aware of before requesting an IP block from someone who has a block of 8
1) Many systems can be run on a single static IP... Mail servers / web servers etc. Is there a specific reason you need more than one? With a bit more info on what you are trying to do it may actually be possible to do what you want without changing
2) Most home based routers cannot route multiple IPs to systems behind your routers firewall and still support NAT / firewalling. If you use the router for DHCP (to supply local networked PCs with IPs) this could be a problem. What router  / additional firewalling equipment do you currently use and we can probably tell you if it supports multiple IP?
3) A block of 4 IPs will actually only give you one additional IP to use. 1st IP is the network address, 2nd goes to the router, 3rd is free and 4th is the broadcast address.

[#4]

Thanks Jake and Peter.
With the help of the excellent support teams on the phone, I've sucessfully moved over to a new block and everything is working great.  I have a Cisco 1721 router on the end so it's perfectly capable of handing the different NATs needed etc.
The reasoning behind needing more than 1 IP is to be able to run 2 independant applications, both running on TCP443. Also we need the ability to be able to use different web filtering polices using Opendns which need to "see" different IP's per criteria.
Thanks for your input.
Anthony