No Service with T-Mobile on a GPP activated 4S. Please help!

Hey everyone. First of all, I apologize if this is not the right place to post this, but I've been working on it for days now, and I'm getting desperate.

I have an iPhone 4S that is locked to Softbank. iOS version is 7.0.2. I'm trying to use a GPP interposer from China3GPP to get it to work with a T-Mobile prepaid SIM. It is advertised as working with iOS 7, and I heard a lot of positive feedback from Japanese people in the same position as me.

The interposer allows me to access the phone as if it was unlocked, but my T-Mobile SIM displays "No Service" most of the time. Occasionally, if I remove and reinsert it, it will display T-Mobile, and cycle through "No Service" > zero bars > one bar, repeat loop. My number is displayed as "Unknown," and I am unable to use the phone to make calls or send texts.

Inserting my friend's Verizon SIM into the Phone resulted in "No SIM" where the carrier would normally appear at the top of the Phone, but the iPhone recognized the phone number from the SIM Card, and a new 3G option appeared under Settings > Cellular. My T-Mobile SIM did not provide service on his Verizon Lumia 520.

I've tried setting it up with both epc.tmobile.com, and fast.t-mobile.com APN settings.

Manually choosing T-Mobile or T-Mobile (3G) as the carrier does not resolve the problem. I've tried formatting the phone, and done the GPP unlock process multiple times. I'm completely out of ideas, and I'm getting really bummed . I'd really appreciate any advice.

The GPP interposer I have specifically stated that it should work with iOS 7.0, although I believe 7.0.2 (which is on my device) was rolled out after I purchased the interposer. Could this cause a significant problem?

I went with one from china3GPP first of all because it was recommended by other people with Softbank locked iPhones, and because they indicate that a 4S should be fully functional without any mention of patches. I can't be certain, but it seems like they are the ones who originally create the GPP interposers, and other groups like NeterTeam resell them.

As the china3GPP website is in Chinese (with only poor English translation), I can't find any mention of patches. Do you think NeterTeam's GPP patches would work with my china3GPP interposer?

I'll definitely look into R-SIM 9 as well, although I'd prefer not to have to spend more money.

Solution

Hey, I just wanted to come back to this thread to thank everyone who replied. I ended up getting an R-SIM Air, and after a long wait for it to arrive, had a lot more success. It was simply a matter of popping the new T-Mobile SIM in along with the interposer, and selecting the original carrier that the iPhone was locked to.

To further clarify for anyone else in my position (the R-SIM site has some pretty poor English translation as well), here are a few details.

-My iPhone is locked to Softbank, and I'm running iOS 7.0.2.
-I got the card from the official R-SIM Air website. I've heard older versions of it purchased secondhand are less likely to work.
-In my case, no patching as necessary.
-Before selecting Softbank (JP SB), I had to select "Mode2 (4S ios6&7) 3G"

At this point, I'm green across the board. I hope this info can save someone from the hours of frustration I went through.