I would estimate that I have been 15-20 times over the past 10 years. Never once have I had an issue. Never have I seen anybody have an issue. On occasion I have seen 'special' people who need 'special treatment' that seem to be disappointed but most everybody seems satisfied with the experience.
I set it up while I was here (in Thailand). I had to use a friend's cell phone number and I already had a google voice number. I think, it maybe one google voice number per cell phone number, so I wouldn't be able to use my friend's number if she was using google voice already.
Google voice works for most things, every once in awhile it won't work for verification stuff.
Whatever you're plan, I would have a plan B. Know which flight to KLA or PP you will take in case you're denied entry.
They have been cracking down, I guess. I *think* they're more concerned with people who come to Thailand and doing leave or don't leave enough. It sounds like you are here only part time. I think the Thai government appreciates those individuals who come to Thailand and spend money, then leave, then come back and spend more money.
Last time I came in, I came in on METV (,..Tourist Visa) and I got questioned. The supervising IO said with all the various visa options available now there is no reason to be doing back-to-back tourist visas.
I have been coming in on a long questionable visa history, it usually works out ok for me. I have gotten 'spoken to' a couple of times but they let me in.
Most recently, with a very legitimate visa, they gave me the hassle and this time I think they were serious.
They explained that with all the new visa options there really isn't any reason for doing all this silly visa nonsense.