Currently, there are more and more reports that Congstar is changing its contract tariffs to no longer allow LTE tacitly. This would mean that an exciting feature of the Deutsche Telekom subsidiary's postpaid tariffs would be lost.
Although LTE was never part of the contract with Congstar, it was previously possible to use it with a post-paid contract within the specified speeds (7.2 Mbit/s) - practical when UMTS reception was poor. This now seems to be changing, both in the Phone meeting.de forum as well as on Teltarif.de there are corresponding messages. There is nothing official from Congstar or the Telekom about this topic. So far Congstar, as a subsidiary of Telekom, has been in the special situation of being able to offer LTE - something that other discounters have otherwise been denied.
It is not yet clear what strategy Telekom is pursuing in this regard, nor whether all existing contracts will be converted. So far, it seems that LTE is no longer possible only in the case of a new contract or a tariff change. With my own contract with Congstar there are no problems to use LTE with an iPhone 5 today (17.02.2014) - the speeds are still good, the device logs in via LTE. Probably the Telekom wants to market LTE more as a premium product, so it's not a good idea to get it at your own discount store (even if at a reduced rate).
In principle, it would be a pity if Congstar lost this unique selling point. Many customers will then probably consider whether they should sign a contract with Telekom or rather with one of the three other network operators. It would at least be a nice gesture if LTE were at least retained for existing customers - even if it was never part of the contract. As long as there is no statement from Congstar, one should at least not conclude a contract with Congstar with LTE as the main reason.
Apparently, it is now the case that Congstar would still allow LTE, at least in existing contracts and in the 9-cent postpaid tariff, throttled to 7.2 Mbit/s. LTE is no longer possible in the Allnet flat rates.
Even more than a year later, a Congstar Smart tariff still allows you to benefit from LTE. Although it is still throttled at 7.2 Mbit/s, people on the move in particular benefit from better network coverage: where others only get EDGE, Deutsche Telekom has already expanded LTE in some cases, which then also benefits Congstar customers. In general, the latency is also lower, so you get a faster "surfing feeling" than with 3G/UMTS.