hat all countries in the Union use the same frequencies. Thus, European countries provisioned GSM in the same portions of the airways and manufacturers developed multiband devices compatible with the frequencies that were allocated. Most GSM phones are either dual- or triple-band and are capable of operat- ing on various GSM frequencies, including 900MHz, 1.8GHz, and 1.9GHz, as well as 2.1 GHz and 2.6GHz 3G and 4G protocols. In the United States, carriers such as AT&T Mobility and Verizon Wireless offer multiband handsets for lower 700MHz and 800MHz frequencies and higher 1.9GHz frequencies. Multi-mode Devices Most digital mobile handsets are tri-mode or quadruple mode. Tri-mode phones oper- ate with three air interfaces; for instance, GSM, Wideband Code-Division Multiple Access (WCDMA), and High-Speed Packet Access (HSPA). Quadruple phones oper- ate with four different air interfaces, such as GSM, WCDMA, HSPA, and LTE. When callers are in GSM areas, they lose speedier Internet access and other advanced fea- tures associated with 3G and 4G cellular service. Managing Security and Billing for Mobile Devices in Enterprises Many enterprises pay for the mobile devices that employees use to check their e-mail and access enterprise applications remotely. These are seen as legitimate business expenses that enable employees to be productive in more locations, for extended peri- ods of time. In the past, enterprises have specified the types of mobile devices that they Handheld Devices and Tablet Computers would subsidize. Often these were BlackBerry devices. This was because Research in Motion (RIM), the manufacturer of the BlackBerry smartphone, offers an e-mail server that has strong encryption and integrates with Microsoft Exchange for e-mail and the ActiveSync protocol. It is also compatible with Cisco Systems's IPsec VPN for secure access to enterprise files and applications. IPsec is a security protocol that creates an additional layer of security during remote access to corporate files. In addi- tion to secure acces