Program errors out if SIM can't support 20 messages.

[xathon]

gsmHat/gsmHat/gsmHat.py

Lines 540 to 543 in f8e4bf7

	if(self.__smsToRead == 20):
	self.__smsToRead = 0
	else:
	self.__smsToRead = self.__smsToRead + 1

This codeblock assumes that a SIM can always store a total of 20 SMS. However, this isn't always the case. The output of AT+CPMS="SM" should be used to determine the maximum storage, since the HAT will raise an error if a slot that's too high is access ed.