I signed up with T-Mobile withing a few days of i-wireless announcing that they would end their service by september 20, 2018.
I don't know how many subscribers are on I-Wireless but I hope they do the changeover sooner rather than later.
Couple things to watch for:
If you were purchasing phone at I-wireless you want to amke sure they know that when you call to switch.
Any Phone we purchased at i-wireless will "likely" be treated as BYOD Bring your own device.
If you want a t-mobile number I would ask them to "port" the iwireless number over, especially if you are doing installments on phone at i-wreless. Then change the number in a few days. Their are reasons I state that but don;t want to step on t-mobile toes
I have spent about 5-6 hours getting my two phones transferred, but I had some odd setups so should be MUCH shorter time fro average i-wireless users transferring over.
The service and support from T-Mobile is equal or better than what we had at i-wireless.
In my case I had a BYOD, and they needed to walk me through the settings for APN to allow data to work.
This occurred only after 3-4 weeks and just after a message indicated tha a configuration profile had to be updated. The following day I did not have data, but their 2nd level tech support walked me through settings.