While working on the Android port of FrontlineSMS, I currently come across the question, what the limits for SMS delivery are (per hour and per day) - and when you would need to consider a bulk service like IntelliSMS. It affects the way the software needs to be designed, and we might need to put a delay between each SMS in order not to hit the limit too fast.
The Android platform itself limits SMS delivery to 100 per hour, however, it can be circumvented by rooting the phone (and loosing the guarantee at the same time unfortunately) and changing a specific system setting. So technically, this hurdle can be mastered, but the next one is the limitation set by the mobile carrier then.
I found that some mobile carrier provide business subscriptions (i.e. http://www.azerfon-vodafone.com/en/corporate/products/bulk-sms/) where there are almost no limitations, while regular private subscriptions usually don't allow more than 100 sms per hour. Depending on each use case, this can either be few or a lot.
The downside with IntelliSMS and similar providers seems to be that it requires a data connection (usually http or smtp interfaces are provided).
I am based in China; referring to these two articles:
the limitations by all three mobile carriers in China are (for regular subscriptions):
China Mobile / China Unicom / China Telecom:
200 messages per hour
1,000 per day
500 messages per hour
2,000 per day
I am interested what limits others users have experienced with other operators around the world.