If you’re a Simple Mobile subscriber and the proud owner of a Samsung Galaxy S6 or S6 Edge, you’ve probably run into issues getting either 3G+ data service or MMS working. SimpleMobile tech support is about as unhelpful as it gets and, personally, I gave up using them after the 3rd or 4th call that ended with “your phone is simply incompatible”. This was really frustrating as I was told pre-sale that my unlocked (Sprint) S6 was fully compatible thus how I ended up with post-sale problems.
No data connection
Despite the huge amount of well written documentation by Simple Mobile (sarcasm), the APN to use can be either “simple” or “fast.t-mobile.com”. The most important piece here is to force the use of the GSM band. To do this, go to Settings->Mobile Networks->Network mode and select GSM/UMTS. This will cause a reboot, and at some point after the reboot you’ll notice you have data at 3G speeds. I haven’t figured out how to leverage 4G LTE (if that’s even possible with Simple Mobile service). Note: I could not get my phone to work with the suggested IPv4/IPv6 APN protocol setting, I had to place it as IPv4 only to work.
MMS isn’t working
In your APN settings, set the following:
APN type: default,mms,supl
APN protocol: IPv4