Voda one is hit and miss, try sending open/close messages at 5pm when thousands of businesses are closing.
And more importantly the Vodafone sms centre could be pulled at any time, how anyone can "sell" that is beyond me.
I am not going to get into the debate over different costs with different forms of signalling but here are two examples where sms via pstn is VERY good.
1. Customer has bells only system and r/a decides that is fine, to have sms alerts as an "extra" in the event of an alarm condition would cost nothing if the system does not trigger. In the event of an alarm consumers will be happy to pay 50p per text to know about it.
The alternative is a relatively costly gsm unit (£200+), monitoring (£60+p/a), or auto-dialler (£100+).
2. Customer has redcare gsm monitoring on his grade 3 alarm system. due to several regulations in place there is a strong likelyhood they will receive the text on their phone faster than the phone call from the alarm receiving centre, and in the event of the keyholder attending the premises having live text alerts of "new" alarm events could be extremely helpful.
In both of these situations the cost of the sms call is next to irrelevant.
Even for open close messages, many systems have just one user that sends open/close messages and just a few times a year, the sms via pstn system would cost just a few pounds per year to monitor that persons open/close messages, with no contracts or other costs than the 50p call (dropcall not pence per minute). There is no other service that can do that for the same cost.