Spark New Zealand (ASX:SPK, NZE:SPK) said it will block around 300 mobile phones that would be unable to make emergency 111 calls after its 3G network shuts down on March 31 due to manufacturer-imposed limitations, despite being able to make standard calls, send texts, and access data over the 4G network, according to a Wednesday statement.

Most of the impacted mobile phone models are from the ASUS range, and some of these can remain connected if a software update is completed. Phones that are not updated or do not have a software update available to them will be permanently blocked from the company's network on March 31.

It said the decision to block these devices was informed by the 3G network shutdown in Australia.