Default Financed and clean imei question

Why is it that whenever i put my sim into a financed tmobile phone (checkesn says financed) it basically gives the phone a clean imei and checkesn results change to activation ready
Current phones: Galaxy Note 3 & iPhone 5.

Laying around in drawer: x3 Galaxy S4 , iPhone 4 , mytouch 3g slide, Lumia 521 , HTC inspire 4G ,& Some more.

My tutorial on how to install international miui v5 rom on T-Mobile S4: