Melbourne electrican Paul Riordan runs a small business employing three people and says his mobile is critical to his business.

"I couldn't function without it. I'm on it eight hours a day," he told SBS News.

"I'd say it's probably one of the most important tools in managing a business."

But Mr Riordan was forced to function without it when Telstra's network went down for about four hours two weeks ago.

"I had two teams out in the field waiting for critical responses from me and by the time the phone was operational and they got those responses, I had to pay them overtime to complete the jobs," he said.

"Along with that I had a client waiting on a callback to confirm a job for the next day but unfortunately by the time I got my phone working the job had fallen through."

It was just one of three recent Telstra network outages that have enraged customers.

In a statement Telstra told SBS World News, "The root cause of each of these disruptions was different but we are undertaking a comprehensive review of the network".

"There will always be issues that arise in such a large and complex technology environment," the statement said.

Independent technology analyst Paul Budde said the addition of new technology to decades-old systems put pressure on networks globally.

"Roughly a third of all the mobile networks on an annual basis get outages like this, so it is something that is common," he told SBS News.

"If it happens once, people say 'OK, fine, it happens', but if it starts happening three or four times, then you really start getting nervous."

"Something like $20 billion a year is spent on fixing outages."

Mr Budde said Telstra's network was fundamentally good, but the outages were concerning.

"I think the problem is, if it reoccurs," he said.

"If it happens once, people say 'OK, fine, it happens', but if it starts happening three or four times, then you really start getting nervous because people are very socially and economically dependent on the mobile phone."

Vodafone knows this only too well.

It lost 2.3 million customers following its 2010 network failures but has invested billions of dollars since then.

Over the last two years the telecommunications ombudsman said complaints have fallen drastically at Vodafone, along with smaller declines across the industry.

Mr Budde said the pressure was on Telstra.

"Obviously, the message to Telstra, is for heaven's sake, get your house in order because the stakes are too high," he said.

"Also for them - their credibility, their brand, all of that - it is in their interest to make that happen."

Telstra shares have taken a tumble since the first outage in February and subsequent March disruptions, down about 6 per cent compared with a 4 per cent gain on the broader sharemarket.

However, CMC markets analyst, Ric Spooner said similar stocks have also lost ground.

"I don't know that you can really conclude that shareholders are too concerned just yet about this issue because other similar yield stocks like the banks, Woolworths and supermarket stocks in the same sort of basket have also been under pressure in recent weeks," he said.

Telstra is offering unlimited free data downloads on Sunday as part of an apology, but Mr Riordan said it was not enough.

"I pay excess for the data that I require for the month so I don't believe that giving me free data helps me at all, and especially not on a Sunday either," he said.

Business customers can contact Telstra for compensation, which it says it will consider on a case-by-case basis.