It's not stopping or even slowing down. Consumers' adoption of mobile banking keeps rising every month, according to the latest results of American Banker's Mobile Banking Intensity Index. Bank customers did more of pretty much every banking task available on their mobile phones in September as compared to August.

A few bankers wrote in to say that mobile banking is getting more popular every day.

"As our banking customers continue to learn about and implement the mobile app, the volume of customers using our mobile app is continually increasing," one surveyed banker wrote.

"As the apps develop, user uses change," wrote another. "Uptime comes from apps being better."

A third cited back-to-school volume. "Kids heading back to college saw an increase in activity in late August and into September," said a fourth.

The index is a product of American Banker's regular surveys of banking executives and is published in partnership with Verizon. The MBII is a diffusion index. For context, readings above 50 in a diffusion index indicate expansion and readings below 50 point to contraction. The further from 50 a reading is, the stronger the indicated change. A reading of 50 suggests that activity was unchanged month to month. All the data in the index is compiled from a survey of 299 bank executives, all from institutions that offer mobile banking. The index values are calculated based on respondents' answers to questions about customer activity in certain aspects of mobile banking, such as checking account balances, transferring money between accounts and paying bills.

Several bankers this month reported that mobile banking was a relatively new offering for them. "To compete, we had to have it," one wrote.

The biggest change in activity recorded in the index was to the volume of activity from retail customers using a mobile device to manage their investments: this rose 13.7 points to 78.7. Perhaps some post-vacation college savings or retirement planning was underway. The sheerest drop in value occurred in the average transaction value from retail customers using a mobile device to make a bill payment, this was down 8.4 points to 64.8. However, this amount does jump up and down regularly; it's not clear that all the bankers surveyed have access to this information.

Downloads of mobile banking apps ticked up 1.9 points to an index value of 79.7. This is a high rate of increasing activity, given that most of the bankers in the index have offered mobile banking since April.

Downtime was down overall for the month. However, a few surveyed bankers experienced glitches. "Vendor issues associated with IOS 7.0 resulted in application downtime," one banker wrote. "We experienced higher than usual down time due to systems-related issues," another said.