I just read through the archived records, and I see I'm not the only one with a poor signal on the 2nd highest floor of my condo, but most replies are 2 - 3 years old..

As one writer suggests, signals are normally pointed to the ground. My hall echoes with folk shouting down their phones or walking around looking for a good signal.

Anyone have any ideas on a booster for within these concrete walls, apart from finding a new condo at a lower level?

A well-reviewed product called WeBoost can make a difference, but it's pricy at about $600 USD, and I'm not certain of its availability in Thailand. I installed two on our campus here in Kuala Lumpur and am very pleased.

Moved to the Internet/computer forum.

see this wiki on how to boost cell phone reception, may help you

http://www.wikihow.com/Improve-Cell-Phone-Reception

I have used this vendor's booster systems before, with very good results: http://www.hispeedaircard.com/

Make sure you buy one appropriate for your cell provider frequency.

see this wiki on how to boost cell phone reception, may help you

http://www.wikihow.com/Improve-Cell-Phone-Reception

Thanks for this. It's answered everything I needed to know.