A priori too little RAM

Except that the 45b has only 512MB of RAM against 1G for 45. That is what is most likely the most limitatitf: after quite some time installing applications that run in the background which implies the need to empty memory in order to launch a new application.
During an incoming call, it also has a little trouble to win: the screen remains black for a "little" time.

In SIM dual use, impossible to choose the preference for outgoing calls and SMS - that the DATA channel can be selected.

Too bad for a product that is otherwise pretty good bill if we disregard the battery too small (like many devices).
Two stars so because I can not say "like" .after two weeks of use.