If I may say somthing here.. we always seems to point fingers at our networks.. and I cant say I blame people....(hehehe most times they deserve it) however, anything to do with international traffic via GSM or cellualr depends mostly entirely on the other network/networks/PSTN/PLMNs...and or SP's (intermediaries)
From the info avaible on the internet it seems India has a bit of a coverage problem as there is no standard Network that covers the entire country , each network covers segments of cities.. also a lot depends on the network infrastructure and their technological standards compared to South Africa's.
Some network even make business decision to to send or recieve international sms's and some even charge you for recieving international sms's while on their network.
So for late international sms's, call the network here Vodacom as ask to see when they recieved the sms. Log a call, and make them work for their money
PS you must get a reference number from them... Get a full name as well..