By selling T-Mobile to AT&T, Deutsche Telekom retains a foothold in the US market while AT&T will greatly bolster its ability to provide improved coverage now. It also accelerates its ability to roll out "4G" HSPA+ technology that Apple's iPhone 5 is expected to support this summer, thanks to new Qualcomm MDM6600 baseband chip already in use in the Verizon iPhone 4 model, which latently supports HSPA+ and will expose functional support in the new AT&T model this summer.
Both AT&T and T-Mobile have already begun building out HSPA+, the latest generation of GSM/3GPP mobile networking supporting data speeds of up to 21Mbps (as some European carriers have been operating for years). Existing AT&T iPhone 4 models support 7Mbps data downloads, and HSPA+ networks can be backwardly compatible with them; new iPhone 5 models are expected to be able to take full advantage of the fast new network.