An insider said: "Siobhan met up with Mutya for the first time in ages over the summer and they got on well. Now Mutya is convinced the original three could be huge again.
"She was on the phone all last weekend trying to convince the girls to reform. Siobhan's considering it."
Keisha - who was the last founding member of the girl group to leave last month - is also eager to reconcile with her former friends.
Another source told Britain's The Sun newspaper: "Mutya is very keen to do this. Keisha has her solo career on the go, but she feels more comfortable as part of a band.
"There were arguments in the past, but all three realise it was because they were young, headstrong and finding fame hard to cope with."
Keisha, Siobhan and Mutya formed the group in 1998. Siobhan was replaced by Heidi Range in 2001 and Amelle Berrabah - who is currently being treated for nervous exhaustion in hospital - took over from Mutya in 2005.
Jade Ewen was given Keisha's spot last month.
The original line-up is now reportedly planning to reform in time for the release of the Sugababes' new album 'Sweet 7' on November 23.