I've used the included Iphone sat texting quite a bit and also carry a Zoleo.
There is no comparison between the two when the shiit hits the fan. Break your leg, being immobile, then try following satellites with the phone..... Or better yet, have a chest ripper, pull out the iphone, wait for it to connect, then get the message, "next satellite will be in range in 12 minutes".
The iphone sat texting is great for telling buddies you have a bull down, it's not an emergency sat device, not even close.
The t-mobile star link setup may be a lot better, I haven't used that.