Current phones generally use only one antenna taking one stream of data at a time. LTE Advanced devices will also need more energy storage to do the necessary onboard computation. Without new breakthroughs in batteries or reductions in power consumption by other means (see “Efficiency Breakthrough Promises Smartphones that use Half the Power”), phones will simply get larger.
via For superfast 4G LTE Advanced smartphone and tablet connections, AT&T, Verizon, Sprint, T-Mobile plan new network tests, and rollouts use chipsets from Qualcomm and others | MIT Technology Review.
Will ubiquitous mobile data bring down its cost for low bandwidth users? We shall see.