Quote

- Wireless Modem Initialization Sequence: The initialization sequence performed in versions 1.44 and older is insufficient in some screnarios (certain 64k SIM cards, SIM card configuruation, etc). The key to the modem being functional is to wait for a “+WIND:#” (1, 4 sometimes 9) status before issuing other commands. The time needed to wait for a +WIND response will vary depending on the SIM and/or network. Waiting a minute is usually sufficient, but up to 3 or 4 minutes may be required. “515” errors are an indication that commands were issued before +WIND 1/4 was reached.

The new logic is:
--1)Send AT+CFUN=0 (graceful shutdown).
--2)Wait for “OK”.
--3A)If no “OK” received within 15 seconds, do a hardware reset of the modem and proceed to step 4.
--3B)If “OK” received within 15 seconds send AT+CFUN=1 (soft reset of modem) and proceed to step 4.
--4)Wait for +WIND response before proceeding with remaing modem commands.
--5)Proceed with remaining hard coded AT commands used to setup text mode, character set and etc.
--6)Proceed with any User defined Initialization Strings defined on the Cellular Modem setup menu.