YEP, that's the reason why SMS messages are delayed for minutes hours (carrier dependant) BUT
U must have in mind that SIM card (were SMS are stored by default) has 20 memory location for only SMS if you try to send more, the answer becomes an "ERROR" instead and you wont know what exactly happen, if you really want to know what happen you should check GSM coverage !
please don't forget saving your phone settings using:
AT+CMGF=1 <CR><LF>
AT&W<CR><LF>
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