If I'm sending an SMS from my app using SmsManager and the SMS fails to send, does the SmsManager automatically retry sending SMS for me - or do I have to manage this myself in code?
no it does not.
if there is no signal to send a message and it fails.. the phone SHOULD automatically continue to try resending..
currently it simply reports that it has failed and puts it in a list of failed messages.
so, no...You can catch if the message was sent or not and repsond to these events.