T-Mobile is to offer a WiFi calling service to corporate users which auto-switches BlackBerry handsets to its mobile network when moved out of hotspot range whilst making an internet call reports mobiledia.

T-Mobile unlike AT&T is a totally wireless operator that will not cannibalise fixed line revenue, while AT&T tries to protect their traditional landline business.

T-Mobile has stated that their WiFi Calling with MobileOffice service enables customers to cancel their landline phones and thus save money on calls.

T-Mobile is the 4th largest wireless carrier in the US and has in recent years been struggling with competing against the likes of Sprint and smaller carriers while AT&T and Verizon have attracted custom.