using dialog or dlg makes your life easier.

-> Counting calls with htable and replicating with DMQ to other node
(can the data survive from a restart?)

htable can write back to the database. But that solution needs a bit more (getting the data - manually or via dialog/dlg and replicate that htable, how to work with htable)?

As an untested idea - you can define two htables. One htable_nodeA the other htable_nodeB. 

Node A writes only into htable_nodeA and vice versa. So there should no race condition.

And then you may check htable_nodeA customerX calls and htable_nodeB customerX calls (sum that) on new calls.

Many ways.

Kind regards

Karsten