Thousands of music-lovers have been piling on to ferries to the Isle of Wight for the first of the major summer music festivals.
Rumours have started to spread that Geldof will join Bon Jovi on stage in the festival climax on Sunday.
Speaking to Absolute Radio, he said: "I know this sounds really matey but usually when he plays here, I get up on stage and do a tune with him because he is a mad Rats fan."
When asked if he would do the same at Isle of Wight, he said: "Maybe, maybe. Say no more."
Speaking of Jon Bon Jovi, he added: "He's a seriously good guy and he has been a good friend. And for all that stuff that we have done, like Live Aid and Live 8, he has pitched up and done it whenever we have asked him with the full band.
"When he comes over, usually I get up and do a Rats song with him because he likes doing them. So I am really more than happy to do warm-up for a mate."
When asked how it was when the Rats got back together in the rehearsal room, he said: "Yeah, awkward, after 27 years of everyone going off their separate ways and going around the world doing this, that and the other - all coming back and the only foundation you have together is this music and this band.
"We were glad to see each other and you have a coffee and that, you're having a bit of craic, but the jokes are all from 26 years ago or 30 years ago, whenever we started in '75. And then suddenly you are playing and that brings it right up to the moment."
Festival-goers have been promised by the organisers that there will not be a repeat of last year's scenes of chaos when heavy rainfall turned the car parks into mudbaths.