I text with people who use multiple phone numbers. At this time conversation is spread into multiple threads and I have to manually switch between them in order to send a reply. It would be nice if I could see all messages aggregated into single thread.
I am aware that there are use-cases that need to be managed - what comes in my mind right now is:

1. label for each received sms would have to include phone number (or its type according to contact list) - it's visibility may be configurable

2. user would have to select a phone number (to which he want to send sms) in order to reply

3. one would maybe like to configure only a subset of phone numbers from a contact from which he would like to see grouped messages