Is it possible to register two sim cards and have two numbers in Thailand with one passport? 

One number for the wife and another for the girlfriend.

Good idea.

❤????????????

So long as the both SIMs are registered, it doesn't matter if you have 2 or more. There's no stipulation on how many times you can register a different SIM using the same passport, so long as its registered and a photograph is taken of your passport, and then uploaded to the NBTC servers from inside the shop using their smartphone app. The question is: why would you want to have more than one SIM? Are they for different phones or for other reasons?

37 minutes ago, Senior Player said:

The question is: why would you want to have more than one SIM? Are they for different phones or for other reasons?

Some people have two SIMs (usually one on a different carrier) when they have signal location issues, or are trying to avoid having their 'clients' pay an out-of-provider surcharge for calling them.

3 hours ago, RichCor said:

Some people have two SIMs (usually one on a different carrier) when they have signal location issues, or are trying to avoid having their 'clients' pay an out-of-provider surcharge for calling them.

A nice out-of-the-way Snapchat account could come in handy, I suppose.  

Many of the Thais I know just subscribe to wireless Internet and use the free voice calling provided by their social media app (LINE, FaceBook, FaceTime, etc) as their alternate number.

22 hours ago, RichCor said:

Some people have two SIMs (usually one on a different carrier) when they have signal location issues, or are trying to avoid having their 'clients' pay an out-of-provider surcharge for calling them.

Yes, that could be a reason, but I was wondering why our OP needed two. To be honest, I don't know why I even bothered replying, especially as this sort of question could easily be answered in a second just by popping into a phone shop or a 7-Eleven.