They are different in some respects and the same in other respects…..if you mean is there any difference in area coverage, signal strength, availability in particular areas etc , there is no difference, BT is a MVNO (Mobile virtual network operator) on EE network, if you mean they have different tariffs, different consumer offerings, then they are different.
if your question is why have two brands , they did try to eliminate BT as a consumer brand and encourage BT Mobile customers to transfer to EE , but a change in senior BT Group management seemed to reverse this strategy and now BT is to remain as a consumer brand .
Can you swap between them , it’s probably difficult to move from EE to BT , but easy to move from BT to EE because of that original decision to get customers onto EE .
