 the same phone is not supported by the LTE services offered by the operators in their home countries or countries of travel. If standardization efforts are not able to narrow down and harmonize the frequencies to be supported across geographies, the onus then tends to fall on the UE manufacturers to support multiple bands. This may increase the cost of production and maintenance for the manufacturers and increase processing capacity, which, again, affects and imbalances the ecosystem. Higher UE costs may imply a larger barrier for user adoption and will also make it imperative to create business plans that will recover investments and work against operators' efforts to provide the best services possible at the lowest cost per user or serviced bit. Note The cost per bit and other items like average revenue per user are discussed in more detail later in this chapter. Voice Over LTE Implementation In spite of the usage of data catching up with traditional voice offerings, as networks have evolved from 2G to 3G and LTE, voice still plays a prominent role in the product to be supported by an operator. Voice is of so much importance that LTE has evolved specific options and solutions to support it. For those operators who want to optimize their networks for higher data performance and offload voice processing, there is the option of circuit-switched fallback (CSFB). In this solution, the operator hands the UE over a 2G or 3G network to support voice, while suspending the active data connection with the LTE network. This implies CHAPTER 3 DEPLOYMENT CHALLENGES IN EVOLVING 4G that the operator needs to continue to support 2G and3G networks, including their legacy core network elements. Such solutions may not appeal to the service-conscious business user, for instance, who expects all services to be available without interruption all the time. Note See Chapter 1 for more details on the key KPIs defined by the Third Generation Partnership Project (3GPP) that need to be supported by systems to help manage QoS. Voice over L