Aaron - thank you for starting this thread. I wouldn't have made the plunge to buy an Icon & try it on T-Mobile without you
. I created an account to pass along my findings - the Icon on T-Mobile where I live isn't perfect, but I think what isn't working can be fixed. I've been playing with this for about a week.
My situation is similar to 7kubo's. I didn't need to manually change anything through Access Point (I've confirmed identical behavior with and without custom settings). The setting that affects mine most is the speed (LTE/3G/2G). Basically, you can pick any two of: fast data, reliable data, or SMS. I have a theory & I'm hoping by knowing the area where folks live we can understand how towers affect the issue. I live near Seattle, which is a refarmed area.
At 2G, I get consistent SMS and data but inordinately slow speed (~200 kbps).
At 3G, I get (what I consider) "fast" data - nearly 10 mbps download, however SMSes consistently fail with "SMS error 1".
At LTE, my phones get the same speed as at 3G (when it works), but are continually bouncing between towers, as described by Aaron. SMSes typically send, but occasionally fail, which probably corresponds to if it's looking for another tower when I send the message. My phones seem to work "better" after the 8.1 update, and my suspicion is 8.1 is just better at finding towers when connections cut out, because it still definitely hops between towers and occasionally fails SMS and data.
I have two phones, and today set one to LTE and the other to 3G. The LTE one drained the battery dramatically faster than 3G. I suspect it consumes more battery to be always looking for a signal.
My SMS error seems to be identical to an issue with reported on T-Mobile forums with unlocked Lumia 822s:
Nokia Lumia 822 can not send SMS over 2G | T-Mobile Support. Unlike this thread, in my call to T-Mobile support I was told they expect any 3G/4G phone to work, and they were willing to work with me to track it down.
Since Superhyper got it to work on 3G, I suspect the farming status of where you live is in play. Superhyper - do you know if your area is refarmed?
Note - I've also been unable to make tethering work, but I'm first working on SMS since that will be a dealbreaker.