Most services are dynamic. If it's static, that's usually a selling point... so they would probably tell you in their list of "features". There are some that give you a static IP standard.

However... I have 2 adelphia cable connections... the IP's are dynamic... however they only ever seem to have changed it I changed the device that first plugs into the dsl modem with a diffrent MAC address. So for about 2-3 years now... my "dynamic IP" hasn't changed. But it could at a moments notice since I'm not paying for it to stay the same. Each network is diffrent. Some places change it on you on a schedule, every 5 days maybe.