There are 3 ways to increase ARPU (get more wallet share) and decrease churn (get stickier with the customer). One way is to upsell the customer like from T1 to 10MB or broadband to EoC.
Another way is to cross-sell. That usually means something like voice services to data customers. It can also mean selling a strategic partner's services like data backup or managed security to all customers. The best examples of cross-selling comes from domain providers like GoDaddy, who won't let you simply buy a domain. It is 8 more screens of options. Oh, and Vistaprint is the same way with a sale of business cards.
Bundling makes selling easier because you put together a valuable set of services priced attractively.
The newest bundling is around business Internet access with Office 365, Hosted Voice and Collab.
The slides from my Bundling for Sticky Profit session at FISPA Live in NOLA are available for $3.