ただいま～ at the beginning


I saw ただいま at the beginning of two expressions and I couldn't understand its
meaning in the context.

> A : すみません。かいがいじぎょうかのぱくさん、おねがいしたいんですが。
>
> 受付：おやくそくですか。
>
> A : はい。
>
> 受付：ただいまおよびします。しょうしょうおまちください。  
>  もうしわけございません。ぱくはただいま電話中ですので、こちらでおまちください。

What do ただいまおよびします and ただいま電話中 mean?  
And is there a rule about ただいま in grammar?




I shall explain each word as I am not sure of your level, or how much of the
sentence you understand.

> ただいまおよびします and ただいま電話中

およびします is a humble way to say よびます (polite) / よぶ (plain), to call (someone).
If you are unfamiliar with humble conjugations and keigo and you would like to
learn more, please visit [this
site](http://www.guidetojapanese.org/learn/grammar/honorific) (hard!).

電話中 means currently on a call (電話{でんわ} phone; phone call + 中{ちゅう} currently).

ただいま, other than a greeting meaning "I'm home!", can also mean "right now".
(See comment by Shoko below)

Putting it all together:

> ただいまおよびします
>
> _I will call ぱく right now._ (Edited)
>
> ただいま電話中
>
> _ぱく is currently on a call._

* * *

> and is there a rule about ただいま in grammar ?

In these cases, ただいま is used in the sense of "right now", as an adverb.
Adverbs often can be placed in many places in a sentence, but it is usually
immediately to the left of **the word it is describing** (currently
**calling** = ただいまおよびします; currently **on a call** ただいま **電話中** )

