Spark, formerly known as Telecom, was now a pure telecommunications company and was subject to the intense competition of that particular market.
The result was ''nothing too serious'', but the share price fell slightly during the day, he said.
In line with other companies, Spark produced a confusing set of accounts, including normalised figures.
However, in the report to shareholders, the company said its revenue for the six months fell 2.7% to $1.79 billion from $1.85 billion, its operating profit was down 3.5% to $436 million from $452 million and its reported profit was flat on $147 million, thanks to paying less tax and lower financing costs in the reported period.
The dividend was up 1 cent per share to 9c.
Mr Timms said after adjusting for rebranding costs of $11 million, the first-half result was below his estimates by 2%.
The key revenue variances were softer mobile service growth, partly offset by strong IT services growth.
In the underlying operating costs, the 1% miss versus forecasts was spread evenly.
Spark chief executive Simon Moutter said the results reflected the ongoing repositioning of the company and the execution of its long-term strategy.
There was sustained growth in good quality mobile connections, up another 108,000 in the period since June 30 as Spark continued to close the gap on the competition.
Total mobile revenue grew by 2.4% but the market remained competitive - particularly in the business segment where revenue fell on the back of continuing price reductions and data bundle expansions.
''We have also upped the ante in the emerging online TV market in New Zealand with Lightbox TV which launched on time in August 2014 - well ahead of competition - to very positive customer feedback.''
Lightbox also formed a strategic joint venture with online sports company Coliseum, which had the rights to PGA golf, French rugby and the English Premier League, to form Lightbox Sport, he said.
The focus during the second half of the financial year would be maintaining intensity of execution, reflecting Spark's determination to build on the firm foundation setting the company up for growth.
Subject to the Commerce Commission's decision on backdating Chorus charges, Spark was on track to meet its earlier guidance for the 2015 year.
