Both vodafone and telecom often have delays under peak traffic times. Most
notably around holiday periods (new years eve etc.) but has often occured at
other times as well.
Theres also politics involved around sending SMS's off-net to other
carriers, i.e. Telecom might not allow you to send to vodafone australia.
The recent introduction of number portability also introduces delivery
issues (the carriers themselves don't send to ported numbers, the sender has
to send to the correct carrier). To this end, there is a webservice
(monthly subscription fee to access) that gives you a csv list (full list,
and daily list) of ported numbers.
On 4/17/07, Philip D'Ath
I don't recall ever noticing a lag of hours for SMS delivery (I don't ever recall a TXT taking more than 60s to be delivered) but I guess different TXT processing systems use different methods for getting the TXT into the network for delivery.