Can you get two SIM Cards with the same telephone number?

Yes.

 

http://www.ais.co.th/postpaid/multisimpackage/en/

Yes, I think all 3 major providers here offer variations on this service, sometimes called Multi-SIM, with up to 5 SIMs on a single number.

 

It may, or may not, do exactly what you want so be sure to review the actual terms and conditions.

 

http://www.dtac.co.th/business/en/products/view/18

 

can't find the TrueMove H page

Update:

 

I now have two SIM cards from AIS with the same phone number.

 

1.  Your original SIM card must be post paid, not pre -paid, so the first thing that I had to do was switch to post Paid.  Requires passport, and either work permit, house book or 5 year Drivers License.

2. Once converted to post paid you can apply for the multi SIM.

 

It took about 2 hours as I did it in the small Telewiz shop in the Chainat mall after email discussions with the AIS Call Center which I copied and took with me.  The first problem was  getting them to understand what I wanted, but after reading the emails from the call center they got it.  Then I had to wait for the girl to charge her smart phone as she had downloaded the instructions and the phone was dead.  When I left I didn't;t fully understand the operation as I was getting frustrated but after a couple of emails to the call center I got it.  If you want to receive or make calls  and messages, you must activate the card on the phone that you are using by calling *100#.  You can find out if it is already active by calling *101#. The internet is active all  the time on all devices.

 

I purchased the cheapest option, 399 baht/month for the post paid, 99 baht/month for multi SIM and 20 baht/moth for something else coming to a grand total of 518 baht/month.