Fighting SMS spam is complicated by several factors, including the lower rate of SMS spam (compared to more abused services such as Internet email), which has allowed many users and service providers to ignore the issue, and the limited availability of mobile phone spam-filtering software. Filtering SMS spam at the recipient device would be an imperfect solution in markets where users are charged to receive messages, as the user may still be charged for the message once the provider sent it, even if software on the device blocked it from appearing on the device's display. This problem is not present in most of the world outside the U.S., however, where users are not charged to receive messages.