Thank you for replying. I checked my cell phone(receiving unit), I think it is on LTE which is 4G. so I’m wondering in order to receive the sms message, do I need to change to GSM mode, because 4g is build on the top of 2g, isn’t it?(actually I tried to manually change my cell network mode to “GSM only”, unfortunately, I ended up finding that my service provider , which is Telus, doesn’t provide GSM).
In addition, I don’t think I comprehend what you said “SMS is literally like posting a letter, you push it into the network and there is no way to force or trigger a delivery of it”, did you mean delivering the sms to destination is something out of control by the developer, just depends on the service provider?
BTW, I’m using a sierra wireless sim on WP7702.