The pair had earlier visited the 2degrees outlet in Botany Town Centre, before going overseas, to ask if their phone was capable of making a call in Mumbai.
The staff warned them that call costs would be higher overseas but didn't warn them about roaming charges or that they should switch their phone to flight mode when they weren't making calls, Sue said.
"Shops are manned by young people, totally adapted to the electronic era, who cannot conceive that some oldies do not have these same abilities and need greater explanation on the hows and wherefores," she said.
Sue's husband Bob described the situation as "a trap for novice players" and thought more should be done to ensure older people fully understand the potential costs of using modern smartphones and other technology.
2degrees has now promised to refund about $750 to the couple as a "one-off, goodwill gesture" to cover the roaming costs they incurred in India.
Spokeswoman Katherine Cornish said the Wakelins did the right thing by visiting a 2degrees store for information before their trip and that the company expected staff to explain data roaming and how to turn it off to customers.
She said the Wakelins also received notifications in each country they visited about the company's charges, including 12 texts - four of which were "2degrees alert texts, telling them they were incurring high costs".
However, Bob said the couple hadn't thought it possible to rack up such a large bill because they weren't using the phone and had it off most of the time.
He said the pair "appreciated" 2degrees now waiving the bulk of their bill, but the principal still holds "that if you are going to give advice you should give all the information not just half of it".
The couple's main reason for coming forward was the hope their "salutary tale" would help others avoid the expensive pitfalls that can come from overseas roaming charges.