The creators of SwonSong, which was launched earlier this year, says hundreds of people have signed up to record video and audio of themselves talking about their lives.
David Lamonby, 63, who established the app and website alongside his son Ian, 40, said he has recorded several versions of his own posthumous dispatches.
But while romance is key, he has his mind on practical matters too.
"If the message is for my wife - it'd be a whole load of information. She's not very good financially, so some of it would be what a fantastic life we've had together, but otherwise it would also be this is what you've got to do with the life insurance and the bank accounts and this is where the will is stored.
"I've known so many people who've lost a partner and quite often the one who's gone is the one who's done all this stuff. It is such a good idea to lay it all out," he said.
The pair have spent three years developing the app.
"It's something that I've thought about a lot - there must be a better way to be able to make your departure and send messages like this, and I thought with smartphones, we could develop it," he said.
For a eulogy users can create a presentation, choose an appropriate musical accompaniment to their message and add a slideshow with favourite photographs to play at the end.
Different types of message have different charges. The eulogy is the most expensive, at £16 ($30), which pays for the cost of storing it on the app's servers.
But voices from beyond the grave can cause problems as priests say that an increasing number of people choosing to write or record their own eulogies is causing ructions at funeral services.
Father Christyan James, a parish priest and funeral minister based in Brighton, who was recently named as the Good Funeral Guide's minister of the year, presided over a service with pre-recorded eulogy, which had been made using a laptop webcam and burned on to a CD, a year ago.
"On the whole, people didn't like it very much - I think they were trying to get used to someone not being there and then suddenly they're there," he said.
"It felt very uncomfortable. But she was a lovely lovely lady. She died prematurely and she wanted to say how much she loved their family and what they meant to her."
The idea has developed from the trend for people to write their own eulogies before death, for a family member or the priest to read out.
Sandra Millar, head of life events at the Church of England, said priests were increasingly dealing with highly personal funeral occasions, a trend which dated from the funeral of Princess Diana.
She cautioned that friends or family members should be prepared in advance if they are going to receive personalised messages after someone's death or see a video of the deceased person at their funeral.
"People do need to think about this because death is a part of our lives, it's a reality, and you need to get that balance between helping people remember you well, and realising that that life has come to an end.
"You have to know that you're dead, and you can't keep on being part of someone's life," she said.
Christyan said that in general the growing informality of funeral services had led to increased tensions.
"I've had a lot of services where there's been a lot of difficulty and hatred," he said. "I've actually had one situation where two sisters started physically fighting.
"As a society we're less inhibited. We don't keep our feelings to ourselves any more, we're encouraged to voice them - and people just let rip."
