What would cause a rightward shift of the supply curve for cell-phone services?

A decrease in the cost of production.

Explanation:

A decrease in the cost of the production will cause the supply to increase. As the cost of production decreases the firm will be able to produce more at the same cost.

This will cause the supply curve to shift to the right, as the firm will now supply more output than earlier without raising the cost of production.

This reduction in cost of production may occur because of reduction in the wages of workers or decline in the cost of raw materials, etc.