Mindsight Hypnotherapy owner Garry George said he used Vodafone for his business cellphone and was not receiving text messages from his clients who used Spark for their cellphone service.
''I can text them - and it gets through - but they can't text me back.''
The text messages sent by Spark customers appeared to have sent normally, but never arrived at his phone.
More customers were using text messages to organise business and he was worried he could be losing clients.
''I don't know what I'm missing out on.''
Some Spark customers have had problems sending and receiving text messages since the company performed a planned software upgrade to its text platform on June 20.
When the glitch started, Mr George's clients were not receiving his text messages.
Now, they were getting his messages but could not reply.
A Spark spokeswoman said Spark had a minor issue yesterday with one of the three sectors of its Green Island mobile site, ''which we believe could be related to the issues experienced by Mr George''.
''We realise this is frustrating and sincerely apologise to any customers inconvenienced by this fault.''
Spark was working to source and install the necessary hardware to fix the issue as soon as possible.
Spark had a ''very low volume of queries'' regarding the problem, as many customers it serviced could access mobile services in the area by connecting to one of the other two sectors on the mobile site.
Some customers were also connecting to an overlapping cell site in the area, she said.
