And Spark's budget sub-brand, Skinny, was up 8 per cent (proportionate to its third-quarter share) to 6 per cent.
The TelcoWatch survey is based on the number of unique, active mobile connections for each telco, with machine-to-machine sim cards filtered out.
It's based on data from Modica Group, which runs a text-messaging platform used by clients like Sky, AT, Spark, Fonterra, ANZ and Westpac - which it says collectively gives it an anonymised take on the mobile phone company choice of some 2.9 million New Zealanders.
TelcoWatch says Spark recorded a market share high of 37 per cent in the final quarter of 2018, with Vodafone hitting its lowest share of 35 per cent in the same period.
Since Spark's peak in the fourth quarter of 2018, its market share has continued to decline, hitting a full-year low of 35 per cent in Q4 2019 by TelcoWatch's count, while Vodafone hit a full-year high of 37 per cent over the same period.
In terms of their official numbers, Spark said in its most recent NZX filing - for its financial year to June 30 - that its total mobile connections (including Skinny) had risen 2.3 per cent for the year to 2.52 million.
That put it neck-and-neck with the final figure allocated to Vodafone NZ's mobile operation by its erstwhile UK parent, for the second quarter: 2.54 million.
And well ahead of 2degrees, whose Toronto-listed parent reported 1.41 million total mobile customers in NZ as of September.
What really matters
But while total customer numbers are good for bragging rights, stock market analysts focus on percentage of customers on contract - who spend a lot more per month than those on pre-pay.
For example, in FY2019, the average Spark contract customer paid $42.62 per month and the average prepay customer just $12.48.
So it's the percentage of customers on contract or "post-pay" that is the big deal.
And here, Spark's done well. If finished FY2019 with 50.4 per cent of its customers on contract, a 5.2 per cent gain for the year that helped to underpin its healthy performance on the NZX.
So has Vodafone NZ, which moved from 41.7 per cent on contract in the first quarter of 2018 to 44.5 per cent in the first quarter of 2019 (its most recent figure).
2degrees had 32 per cent of its customers on contract as of September 2019 as post-paid numbers jumped 8.6 per cent, albeit off a relatively low base (from 396,000 to 430,000).
The telco's new CEO Mark Aue recently told the Herald he wanted to lift that figure, in part by targeting the business market, which is rich in contract customers but largely dominated by Vodafone and Spark.
For their part, Vodafone (which launched 5G in December) and Spark (which will follow in July) are looking to build their high-end customer numbers with a focus on network upgrades.
Aue said 2degrees will continue to pep up its 4G network but has no immediate plans for a 5G rollout.
