Just to clarify, if people are getting confused as to why some networks seem to get spammed with these texts and some don't; mobile numbers are assigned to networks in batches. I work for a company related to telecoms and we have a list of all the codes and which network they belong to; for example, 07409 falls under Orange, 07507 falls under T-Mobile, 07810 falls under Vodafone, and all numbers stemming from that are of that network.
It's possible, and likely, that they dial the numbers in batches, in such a way that they all go to the same network.
Of course, this varies if you've had the number ported.