I also have a Galaxy S4 and I get 100% of my SMS texts, the only ones that don't get notified or you can't even see are the MMS.I have a Galaxy S4 and my texts come across about 95% of the time. The sales person told me it should work because it's an Android phone and the iPhone isn't supported yet.
double check the the blue tooth setting on your iphone while in the car, (make sure it's on) and click the little (i) right to "My-car" and turn on the notification. , mine 5s works fineI did that a long time ago. Its still very hit and miss whether I get a text on my iPhone.
could you also send messages back?I have an iPhone 5 (ATT) and I also have the latest software update of In Touch. I deleted my phone out, set a different password for blue tooth, re-synced the phone, and I have received 100% of my text messages via In Touch. Its actually a really nice feature.
Hope this helps.
I have the same experience with my Galaxy S3. Texting will show up intermittently. It will also show up delayed.I have a Galaxy S3 and it's about 50/50 for me being able to review / have my text messages read via the car. I usually don't worry about it until I get to a safe stopping place since about half the time I get the "unable to retrieve messages" alert.