Complex sentence: This network does not support GSM, so only 3G handsets will operate on this network, for people bringing their existing handset to the network or roaming 850MHz UMTS is the key required frequency.
Split into simpler sentences: This network does not support GSM, so only 3G handsets will operate on this network. For people bringing their existing handset to the network or roaming, 850MHz UMTS is the key required frequency.