It is no secret that the cellular mobile networks have been the fastest-growing segment in the ﬁ eld of telecommunications over the past decade. Over 4.5 billion customers were estimated to use cellular mobile services such as GSM, 3G-GSM, and HSPA technologies in 3Q 2009; those using CDMA2000 and 1xEV-DO technologies exceeded 600 million, bringing the number of world subscribers to over 5 billion. However, what content providers and users have been awaiting for many years has now happened: the rapid migration of the networks to 3G or 3.5G technologies and a surprising growth in multimedia handsets and smartphones, creating a new ecosystem of users, operators, and content providers. Over 250 million 3GUMTS handsets were shipped worldwide in 2008 and the number is expected to treble to over 750 million in 2009 (ABI research , Jan 2009). This means that there is an ecosystem of more than a billion 3G users that can be targeted for advanced services. It provides an unchartered territory to users and content providers as they move toward 4G. This chapter is about this new ecosystem.