Telephone No 740 is basically a Telephone No 746 with a different cover incorporating holes for 4 buttons.
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I'm not sure what application this particular telephone was used for but it has been kitted out with many of the possible extras. You will see that there are slots for up to four buttons. The case has been fitted with two lamp opals which occupy the knock-out holes in the cover. The buttons are labelled ON/ OFF and RECALL.
Inside the cover you can see how the buttons are held by pins pressed into the slots in the case moulding. As with the 746, the blank buttons can be removed by squeezing and pushing.
With the cover off you can see that although the brackets are present, there are no lamp holders to light the opals in the cover.
I don't have a Tele 740 with a lamp, but the bracket and nounting is the same as this one on a Telephone No 710.
The device across the front of the bracket is a latch plate. It is used with the operating plungers fitted to the centre button positions. By rotating the small steel forks each button can be made latching or not. Pressing another button will release the latched one. A full description is contained in N848.
The outer positions have Switches 23A-1: the left hand one is latching for bell on/ off; the right one is non-latching for recall. These don't work the latching bar.
The uses to which the Tele 740 could be put were many and various such as data sets, headset operation, multi-line working and so on. An idea can be gained by looking at the different engravings for buttons shown in N849.
Next is the wall-mounted variant, Telephone No 741