[Dave Moll]

"SEC'T" is presumably short for "secret", the opposite being "normal". As to what exactly this means on this 'phone, it may be for use with a scrambler unit for transmitting speech in a manner that cannot be intercepted without the use of a second scrambler to decode it - enabled by pressing "SEC'T", while "NORM" would revert to sending speech in its normal, unscrambled form. Others may be able to correct me here or elucidate further.

Recall is a way of initiating additional functions (usually on a PBX) such as call transfer etc. When RECALL is pressed, dial tone is returned so that another extension or service can be dialled while the original caller is held. Exactly what functions can be used depend on what is provided by a particular PBX.

There are two types of recall: timed-break or earth recall. Again, which type is used depends on what PBX is in use. On the whole, earth recall is used on older systems and timed-break recall on more modern ones.

Presumably, unless the extras are a later modication, the actual model number may be something other than 746. Please can you confirm what is stamped on the base.