An ISP is someone you pay a monthly fee to in order to have internet service. You would have to call any provider you would like to use as your provider to arrange to have their service. You might be able to get Yahoo DSL, if you want DSL., but again, you'd HAVE to contact them.
http://dsloffersonline.com/yahoo_dsl.htm?OVRAW=is%20Yahoo%20an%20ISP&OVKEY=is%20yahoo%20an%20isp&OVMTC=standard&OVADID=10871419521&OVKWID=25649428021