[inquisitor]

During the last 7 days I used my toggle SIM in Chicago in my Samsung Galaxy S5 DuoS. As my German postpaid SIM includes 500MB of data for roaming including for the US, I used toggle for voice only which why I used it on GSM only.
Interestingly my phone sometimes indicated the T-Mobile network my toggle SIM was registered on as "roaming" network and sometimes not. Initially I though that might be owed to the fact that T-Mobile (like all the US networks) use multiple MCC/MNC tuples of which some correspond to the prefix of my toggle SIM's US IMSI and some not. However I realized that the US IMSI of my toggle SIM start with 311-960 which is Lycamobile's MCC/MNC tuple while T-Mobile uses only 310 as MCC and the last network my SIM was registered on was 310-260, so the IMSI prefix and the MCC/MNC tuple of the used radio access network always differed.
Now that I'm back in Germany I was able to read my toggle SIM's EHPLMN list. The "Equivalent Home Public Land Mobile Network" list allows to assign one or more MCC/MNC tuples to a SIM card which are then treated as home network which - if correctly implemented on your phone - are not considered roaming networks any longer. However the EHPLMN list of my toggle's US identity is empty, so basicly every single network should be considered a roaming network since 311-960 (Lycamobile's tuple) does not exist as physical radio access network - instead it will always use T-Mobile's network with some 310-x tuple.
Now I really wonder why my phone sometimes has not indicated roaming for my toggle SIM. Was that a bug of my phone or do Lycamobile or T-Mobile some magic here? E.g. broadcasting 311-960 as a virtual network from T-Mobile's towers? Afaik it is possible to broadcast multiple MNCs from the same physical RAN however not for GSM but only in UMTS.
Service in Chicago was not very reliable - I could not send SMS to a couple of countries (e.g. to Telekom Slovenia subscribers) and some calls were not connected - instead there was an announcement in American English saying that the call could not be completed and that I should contact customer care if I believe this was a mistake. However my tight schedule did not allow to further investigate this or contact toggle. Also I noticed that for outgoing calls there was a strange sequence of distorted dial tones in the first seconds which sounded like the call is transferred through a couple of systems. That's no serious issue but let me wonder what route my calls went through.

Unrelated to above observation of roaming indication I wonder why toggle don't make use of the EHPLMN feature. Today we have to enable data roaming to use toggle for data service within toggle countries since the toggle SIM IMSIs always differ from the underlying local partner MNO's MCC/MNC tuple. However enabling data roaming for our toggle SIMs involves the danger of forgetting to switch off data roaming once we leave toggle countries which can quickly vaporize our balance if our phones start transferring data in a non-toggle country. Even within Europe there are countries where toggle bills data at horrific rates of more than 10 £/MB.
With all the expertise in SIM card engineering Lycamobile has demonstrated with toggle I cannot understand why they don't use this simple and convenient feature.
Please guys, implement a EHPLMN list for all our IMSIs!