This activity introduces students to Activity Center. In this activity, students will explore change in the context of cellular telephone charges. Students will create a scatter plot showing that the rate per minute for a "pay as you go" cell phone plan remains constant, or has a "flat rate". Students will create a second scatter plot showing the total cost based on the number of usage minutes. The concept of slope will be explored as it relates to the cost per minute charge. As a follow-up activity, students will look at another plan that has a lesser minute charge and therefore a smaller slope.