The Alcatel OT-890D is a MT6573 based smartphone. It seems one of the UARTs is available on test pads as seen in this picture:
The voltage level is still 3.3V, so no fancy 1.8V gear is required.
During boot, the UART is first used at 19200 bps, where it prints the strings "MW01" and "MW02". I then switches to 115200 bps where it prints "READY", and finally switches to 921600 bps, where it seems to output some mixed binary/text messages containing AT commands and responses between AP and BP, as well as some debug information:
�Ue� � � T+CREG=2 �Ue�!�!�!T+CSQSQ=1 �Ue�!�!�!AT+CREG=2 �Uew�"w�"w�"SQSQ=1 'Ue""" AT+EFUN=1 SML: Load!_Ue"""""" SML: Load!hU("("("
I haven't yet investigated if the binary between the text is some standard HDLC framing or a TS 07.10 multiplex.
If anyone knows more about the boot process (MW01/MW02/READY) or the binary protocol, please let me know.