The company, which operates the Orange, T-Mobile and EE brands in the UK, said it was "firmly on track" to meet its target of more than one million by the end of 2013.
More than 300,000 customers have signed up for superfast 4G products and services in the five months since their launch by mobile phone operator EE, figures showed.
Many customers using the high-speed mobile web service were now choosing to use it instead of public Wi-Fi or home broadband, as they surfed popular sites including YouTube, Facebook and iTunes, according to a survey commissioned by EE.
The figures for the first quarter of this year showed the firm's 4G customer base had reached 318,000 by the end of March, following the roll-out of the service in several towns and cities since October.
It is the first time the operator has issued numbers since it was allowed to launch the superfast service ahead of its competitors, which will do so later this year.
Emeka Obiodu, principal analyst at Ovum, said the figures were "encouraging" though not "massively impressive". He also expressed caution about figures showing a fall of more than half a million pre-paid mobile phone customers amid a shift towards users paying a monthly bill.
Revenues were also down 5.4% year-on-year - though this was blamed mainly on changes in regulation of the mobile phone market.
Total customer numbers were down over the period, driven by the fall in pay-as-you-go numbers. An EE spokesman said it had since changed its offering to make it "more competitive" on data usage.
Neal Milsom, chief financial officer, said the results were in line with expectations and that the company was "making good progress focusing on high-value segments".
EE said more than 1,600 medium and large companies were now using its 4G services. Double-speed 4G was expected to be available in ten cities by the end of June and more than 70% of the population should have 4G coverage by the end of the year.