If you reset the modem and the IP doesn't change, it doesn't mean it's static, it just means the DHCP lease hasn't expired. It needs to expire while you're disconnected.
http://en.wikipedia.org/wiki/Dynamic_Host_...ration_Protocolhttp://en.wikipedia.org/wiki/Dynamic_Host_...#DHCP_releasing
You may have a 24hr lease from the ISP, but you can still send a release/renew request to get a new IP.
The lease time is used mostly for the occasional disconnects so you can resume without issue (for example if you're downloading or chatting on a messaging client, although after more than a minutes without a connection messaging clients will tell you that you've been disconnected and the server will terminate your connection and log you off). Longer leases are for longer term disconnections (up to the lease time) so that you can return to your previous IP address and don't need to reconfigure a new address for anything that needs an address.
A normal disconnect, or even a reset or power off/on of the mode, will not send a release/renew, for that you will need to leave your modem off for a few moments (~15 sec) for the information in memory to clear so that the modem will automatically get new information from the ISP.
QUOTE(Märk @ Mar 19 2011, 05:35 AM) if your modem is always on to change you ip leave it off overnite then turn it on in the mornin.