An IP based combo can work for you: try to deliver via SMTP over your network at first. If that fails, have a dial on demand POTS modem to another ISP and send via SMTP that way, or fail-over to delivering to 026 via Pacnet with same POTS modem.
Of course, this still doesn't address the reliability issue of SMS, on either telco.
Both SMS and SMTP are best-effort. Thus relying on either for time-sensitive delivery of messages is a risk you need to weigh up. The original query was about Telecom Alphanumeric Pagers. Paging is considered more reliable than SMS (is it? Ive always assumed that) and its used for dispatching Ambulances, for example. An Internet based system that stayed within the realms of 'better than best effort' would need something engineered where you talked directly to the Telecomms Provider network (aka Telecom) and it was transactional - ending with a 'yes, I got your message' (and even better - 'yes, it was sent'). I wouldnt count relay-driven systems (like SMTP) as being in the same boat. Exception maybe if its a dedicated domain or subdomain and direct SMTP to the destination MTA was used, perhaps.... But yeah, nothing beats a 24/7 watch system and the good ol twisted-pair telephone call when all is said and done :P Mark.