I discovered with that both 3g usb modems K3520 -Z and -H (made by huawei and zte) don't get enough electrical power do dial or to maintain a connection.
tried in different sites - so the 3g signal was ok and with 2 different carrier sims inserted.
also tried it with 2 different 703n - so it's a general issue affecting all the v1.2.
strange, the black ZTE modem from rcs-rds works fine, both powered and providing network..
i'm playing with v1.2 too