Some providers don't even offer a static ip to residential customers. IN my area, to get a static you must have the much more expensive 'business' plan.
A great workaround is to use a dynamic dns service (i.e. no-ip.org, dyndns.org). I run a small service on my home server and it will register the IP with dyndns service. So no matter what IP I have at the moment, I can always use somethin like 'myhome.dyndns.org' to get to my connection.
Most of the ISPs provide IP addresses throuh DHCP server only. So you will get IP address dynamically. In case if you really need a static ip you can get it from your ISP but most of the ISPs charge extra for that.
In case you are using a wireless router I guess you will have an option to set a static IP so that ip will not change in your box(PC/LAPTOP/VoIP Phone/Printer). Go through your wireless router's user manual and configure it as per your requirement.
Yes,Static IP is extra charged by the ISP.This is because they dedicate that Ip to a single user so that no one else shares that IP.Dynamic IP is profound to change.If you so necessarily need a constant Ip you can approach your ISP in regard of it.Once you get the Static IP you can reset your modem and confirm that it doesn't get changed using Ip-details.com