Answer:
They will be forced to use Skype software as no alternatives will be available
Once they develop a Skype network of contacts, it will be harder to move to a free network
Skype could begin charging for their service at any time they choose
Skype has deliberately limited capabilities of Skype for non-Intel users (details here)
Skype is provided and runs natively only on the x86 and x86_64 (32 and 64 bit), ARM (iPhone, Android phones) and Power PC (Mac with G4 or G5 processor) architectures, excluding people using other architectures
