I'm supporting SMSC (short message service centers) for the last 4 years. So what I will now tell is something what I know very well. First of all, so called SMS delivery reports refer to GSM Phase 2 delivery reports. In other words that technology is a standard and normally all the SMSCs support it. What the cell-phone needs to do to get that report is just to set a special flag (that is set it 1) when a message is submitted. SMSC receives the message, recognizes report request and sends it to the phone when the message has been delivered. The phone of course must be capable of processing that report, otherwise whatever may happen when unsupported type of message is received.
The funny thing about that is that commcenter software of iphone does support delivery reports. It was discovered by those guys who jailbreack iphones and create a software to extend iphone capabilities. They checked the commcenter code and found out delivery reports are basically supported but not used any how.
In my understanding, there is no reason for Apple not to support delivery reports. I respect USA market, but considering that major cellular operators of North America do not support the feature, Apple shouldn't forget that iphones are sold not just in USA but worldwide. So I believe it is something like a marketing issue which has nothing to do with the technical details
The only thing we customers can do to track a message status is to order GSM Phase 1 reports. It is a regular message which usually contains a text like "Your message to number XXX has been delivered successfully", or "Your message to number XXX is expired" etc. However such notifications may not be supported by operators, because that notification type is not a standard but a pure feature which operators had implemented a long time ago in 1990s to give subscribers more comfort
