Although Wanaka had been back "on line" since 3.30am yesterday, St John station manager Don McMillan said he and his staff had no way of knowing whether people were trying unsuccessfully to phone for help.
Telecommunications plant owner Chorus was also concerned about the potential human cost from the arsons.
The boxes are mini telephone exchanges and control landline telephone and internet connections.
The fires cut 820 lines, disrupting communication for dozens of residents and businesses between Thursday night and yesterday morning.
The cost to businesses was unknown, but Chorus external communications manager Robin Kelly said the biggest risk was for people with medical alarms.
"People doing this kind of thing put people's lives at risk," Mr Kelly said.
Mr Kelly declined to comment on who might have lit the fires.
Wanaka's emergency services had not reported any major emergencies between Thursday night and Sunday morning.
Mr McMillan said it was possible a personal medical alarm or 111 call from a landline might not have been answered.
While St John could not use the internet and fax on Saturday, that was a mere inconvenience.
"Our biggest concern was for people with personal [medical] alarms. We have no way of knowing [if someone wanted help and didn't get it]," he said.
Wanaka Volunteer Fire Brigade Chief Fire Officer Steve Trevathan also said there was no way of knowing if any 111 calls from landlines had gone unanswered.
Wanaka police and Chorus have called for witnesses and Chorus has also stepped up its monitoring of Wanaka's 50 to 60 utility boxes, as well as the main Wanaka telephone exchange.
Two boxes on Brownston St were set alight on Thursday night and another two were set alight on Friday, one on the corner of Anderson Rd and Hedditch St and the other on Kings Dr.
Police said access to the Brownston St boxes was gained using a key or tool and the fires appeared deliberately lit.
Each utility box had an alarm which was activated when the box was opened.
It registered on a central server in Hamilton.
The alarm could be disabled if certain information was keyed in, Mr Kelly said.
Services to the Wanaka police station appeared not to have been affected.
Teams of engineers were called in from Cromwell and Alexandra to help the Wanaka contractor, Downer EDI Engineering, repair the lines.
However, some disruptions could still occur and customers should contact their service provider so any problems could be fixed.
