We received our I-797 NOA (48-month extension) in today's mail. A separate mailing also arrived with the notification that the biometrics are to be re-used, and a third envelope with the online access code. We never did receive a text message, but that was no biggie since this whole thing from start to finish took less than two weeks.
Some comments.
1) Our I-751 submission was well under a hundred pages long, and that included 4 sworn affidavits and several pages of photos.
2) The only financial ties evidence presented were three consecutive years of Federal tax returns (Married filing jointly), one joint car lease, and one shared credit card. That was it.
2) We saved $2,500 by doing this ourselves. The immigration attorney we used for the original K-1 Visa and the AOS wanted that sum to fill-out the I-751 and send it in with all the evidence paperwork that we would have had to supply her with anyway. I'm not saying that using an attorney is a bad idea, but if you're reasonably diligent and have the time you can easily do this yourself and save a wad of money.